Construction of high efficient g-C3N4 nanosheets combined with Bi2MoO6-Ag photocatalysts for visible-light-driven photocatalytic activity and inactivation of bacterias

Vignesh Shanmugam; Anna Lakshmi Muppudathi; Sridhar Jayavel; Kalyana Sundar Jeyaperumal

doi:10.1016/j.arabjc.2018.05.009

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Original article

13 (

); 2439-2455

doi:

10.1016/j.arabjc.2018.05.009

Construction of high efficient g-C₃N₄ nanosheets combined with Bi₂MoO₆-Ag photocatalysts for visible-light-driven photocatalytic activity and inactivation of bacterias

Vignesh Shanmugam^{^a}, Anna Lakshmi Muppudathi^{^b}, Sridhar Jayavel^{^c}, Kalyana Sundar Jeyaperumal^{^a,⁎}

a Materials Science Laboratory, Department of Physics, Periyar University, Salem 636 011, Tamil Nadu, India

b Department of Physics, ERK Arts and Science College for Women, Dharmapuri 636 905, Tamil Nadu, India

c Department of Biotechnology, Madurai Kamaraj University, Madurai 625 021, Tamil Nadu, India

⁎Corresponding author. jksundar50@gmail.com (Kalyana Sundar Jeyaperumal)

Received: 2018-3-4, Accepted: 2018-5-20, Published: 2018-01-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Novel g-C₃N₄-Bi₂MoO₆-Ag nanocomposite with their g-C₃N₄ nanosheets were synthesized by a facile hydrothermal method. The superior photocatalytic performance of gC₃N₄-Bi₂MoO₆-Ag nanocomposite was owing to the interface of Bi₂MoO₆/Ag nanomaterials whereas reduced the bandgap which enables high separation efficiency, suppressed recombination rate of charge carriers and their high specific surface area (97.4 cm³ g⁻¹). For the MB dye degradation efficiency accomplishes 99.6% within 80 min under the visible light. Significantly, the ideal photocatalytic activity of gC₃N₄-Bi₂MoO₆-Ag composite has 3.63 times faster than pristine g-C₃N₄. Based on the trapping test, the superoxide radical O₂^•- and hydroxyl radical (OH^rad) plays a vital role in dye degradation in chief g-C₃N₄-Bi₂MoO₆-Ag nanocomposite under the visible light exposure. Novel gC₃N₄-Bi₂MoO₆-Ag catalyst has been exhibited superior electrochemical performance, which is smaller charge transfer resistance (impedance), and the prime photocurrent response has confirmed that more charge carrier abilities. The physicochemical assemblies and high degradation efficiencies were preserved after five successive cycles, whereas signifying that the sample was displayed good stability. Based on the consistent energy band positions, the probable mechanism for heightening photocatalytic activity was proposed. This study delivers a visible light driven novel g-C₃N₄-Bi₂MoO₆-Ag photocatalyst is a capable aspirant material and applicable for environmental remediation. Also, the antibacterial activity is well exposed towards disinfection of the bacterial strain, including pathogens which are S. aureus (G⁺) and E. coli (G⁻) bacteria’s.

Keywords

gC3N4-Bi2MoO6-Ag

Nanosheets

Visible light

Degradation

Light-harvesting

High surface area

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1 Introduction

In recent decades, the semiconductor photocatalysis, as a novel intensifying discipline with its primary focus on anatase TiO₂, has fascinated to increasing attention and interest. This is chiefly since this process can directly alter the solar energy into chemical energy upon excitation by a semiconductor. Still, the response of the traditional semiconducting photocatalysts to only UV light vastly confines their practical applications. Nonetheless, the TiO₂ can only captivate the ultraviolet light because of its higher band gap (3.2 eV), which accounts for only ∼4% of the solar spectrum. This outcome was the actual lesser of photocatalytic activity under the sunlight irradiation. In the order to understand of the wide-ranging utilization of the solar light, some narrow bandgap semiconductors such as TiO₂, CdS, WO₃, Cu₂O, AgO, ZnO, and g-C₃N₄ have been proposed to develop visible-light responsible photocatalytic materials (Mao et al., 2017; Zhang et al., 2017; Dong et al., 2018 ). While the great achievements have realized by, numerous drawbacks, including low absorption coefficients, slow redox reactions, fast recombination of charge carries, and poor photocatalytic stability are still limitations of the photocatalytic performance.

Still, the excessive ejection of industrial wastewaters into the environment and also humanity has challenged a great problem in worldwide. Organic dyes are one of the primary groups of water pollutants which are widely used in textile, medicine, plastic, and several industries, still the hazardous belongings of organic dyes (such as methylene blue (MB)) in wastewater have been still a major risk in the environmental problems triggered by them. MB dye is widely used for coloring cotton, paper stocks, silk, and wood has it been applied in medicine as well. Severe exposure to MB can cause increased, vomiting, shock, jaundice, tissue necrosis and heart rate in humans. Because this kind of dyes comprises a high degree of aromaticity, stands for hydroxyl (—OH) and azo (—N⚌N) groups which are non-biodegradable one. Consequently, it is important to develop techniques which are helpful for their remediation (Dong et al., 2018; Katsumata et al., 2014). Hence, the good photocatalytic nanostructured material has extensively used to degradation the organically contaminated water under the range of visible light exposure by means of eco-friendly.

Subsequently, it was moral significance and remains an excessive challenge to resolve the above issues by modifying the effective novel photocatalytic materials, which is targeting at the practical application of dye contained water disinfected photocatalyst and supercapacitors. In recent trends, the graphitic carbon nitride (g-C₃N₄) has wide to interest for photocatalytic and electrochemical behaviors owing to its great features such as narrow bandgap (2.7 eV), appropriate band edge, cost-effective, and long-term reliability (Zhang et al., 2017; Dong et al., 2018; Katsumata et al., 2014 ). To kind of primary stage, the poor electrical conductivity and grain boundary have existed in the g-C₃N₄ semiconductors will chiefly suppress the separations of photoinduced charge carrier. Among, the several catalysts, g-C₃N₄, as unique of outstanding photocatalysts has been widely studied due to its exclusive physical and chemical properties, and high visible light absorption performance and unique belongings than TiO₂, WO₃, ZnO and SnO₂ etc., (Zhu et al., 2017). Accordingly, to can captivate light up to ∼400–450 nm and above, whereas it could suitable band positions, but also own unique two-dimensional structure and outstanding physicochemical stability. Due to its unique electron configuration, superior optical structure, extreme thermal stability, it has typically used in oxygen reduction reactions, heterogeneous catalysis, water splitting, photodegradation of organic pollutants and applied in various energy-related fields in recent years (Chen et al., 2018; Ong et al., 2016). Still, the photocatalytic efficiency of the pristine g-C₃N₄ was limited by high recombination rate of its photogenerated electron-hole pairs. To improve its visible light absorption ability, they induced photocatalytic activity above-mentioned drawbacks, whereas of several strategies have required modifying g-C₃N₄ catalyst. Hence, the preparation of highly active g-C₃N₄ nanostructured catalyst as numerous approaches, such as due to protonation, noble metals and nonmetal deposition with other materials to achieve whereas improving the textural properties (Zhu et al., 2018; Zang et al., 2013). Numerous visible-light-driven photocatalysts have been industrialized, including In, Bi, Ag, Cu, and Au containing photocatalysts. Meanwhile, they have actual effective contained the visible light enhanced photocatalytic achievement compared to other above semiconductors.

Leading, the Bi₂MoO₆ is an innovative enveloped auri-villius related oxide, comprising of [Bi₂O₂]²⁺ layers inserted among the MoO4²⁻ bonds with a small bandgap (2.4–2.75 eV), so is accomplished by capturing in the visible light. Bi₂MoO₆ exhibits photocatalytic activity for organic impurities degradation and water splitting (Li et al., 2014). Hence, the practical application of Bi₂MoO₆ is limited by its poor quantum yield, which is triggered by the speedy recombination of photogenerated charge carrier’s, whereas an attempt to several times to decline recombination of charge carriers.

Even though, the g-C₃N₄/Bi₂MoO₆ photocatalyst, which was prepared by covering the surface of g-C₃N₄ and Bi₂MoO₆ nanomaterials. This heterostructure exhibited remarkably high photocatalytic efficiency for degradation of organic pollutants under the visible light irradiation (Li et al., 2014). In addition to the present work, to overcome the fast recombination progression of photocatalysts, enhanced visible light absorption, large surface areas, and superior photocatalytic performance where general research has been carried out using a noble metallic (Ag) combination of relevant semiconducting materials. Based on the upstairs consideration, the combination of Bi₂MoO₆ with Ag nanoparticles could be realistically fabricated to achieve the exceedingly efficient utilization of solar energy. In the present case of an Ag/Bi₂MoO₆ also gC₃N₄/Ag composites, the key role of Ag metal ions was taken as follows: (i) the composite strongly fascinates the visible light because of Ag has a surface plasmon resonance behavior (ii) Ag serves as electron sinks, to facilitate the interfacial charge transfer in the existing composite (iii) Ag has played bifunctional roles of reducing the bandgap (iv) Ag nanoparticles exhibit natural antibacterial active material.

Therefore, the coupling with g-C₃N₄-Bi₂MoO₆-Ag hybrid composites has strengthening valuable material to achieve the improved visible-light responsive photocatalysis and reduced charge transfer resistance activities. In the photocatalyst system of g-C₃N₄ layered Bi₂MoO₆-Ag composites, by photoinduced holes tend to pass through the valence band (VB) of Bi₂MoO₆-Ag to VB of gC₃N₄ under the visible irradiation, while the electrons pass from the conduction band (CB) of g-C₃N₄ to the CB of Bi₂MoO₆-Ag. However, in the existing case of visible-light irradiation, Bi₂MoO₆-Ag in the g-C₃N₄ lattices can be generated by a high recombination of hole-electrons and less amount of charge carrier resistance ideals (Chen et al., 2015; Vignesh et al., 2018; Reli et al., 2016 ). Hence the photocatalytic mechanism of the photocatalyst composite leftovers far from in clear. The outcomes of experimental values have shown that the prepared g-C₃N₄-Bi₂MoO₆-Ag nanomaterial was exposed to outstanding photocatalytic performance. Additionally, the probable photocatalysis mechanism of the g-C₃N₄-Bi₂MoO₆-Ag catalyst under the visible light irradiation also conversed in details.

Organic water pollutants and further the pathogenic microbial contaminations (bacterial infection) and eradication have the main hazard to mankind as well as the environment severe problematic in worldwide. In precise to concern in hospital-acquired infections, such as door handles, toilet seats and bed rails are the basins of pathogenic microorganisms. Different pathogenic bacteria and the antibiotic resistance by bacteria have become a great challenge in current times. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) are among the most widespread species of gram-positive (G⁺) and gram-negative (G⁻) bacteria, respectively, that bring clinical sections. S. aureus is a human being but also a common course of serious infections, fluctuating from mild skin infections to further serious of life-threating wound and infections of the bloodstream. E. coli is one kind of prime causes of infection at abundant sites in bodies of both animals and humans. The usage of antibiotics is perilous for treatment of the bacterial diseases with their infectious. Novel approaches are then essential to identify and progress the subsequent generation of agents or drugs to regulate the bacterial infections. In the existing scenario, nanoscale material (g-C₃N₄ layered Bi₂MoO₆) have emerged up as novel photocatalytic and antimicrobial agents owing to their high surface area to volume ratio and the unique chemical complexities (Reli et al., 2016) and presently we worked more with Ag on these nanocomposites.

2 Experimental procedure

Materials: Melamine (C₃H₆N₆, 97.5%), Bismuth Nitrate (Bi(NO₃)₃·5H₂O, 98%) were purchased from Molychem Chemical Reagent Co., India. Ethanol absolute (C₂H₆O) and Ethylene glycol (C₂H₆O₂) were purchased from SDFCL chemical Co., India. Sodium Hydroxide (NaOH) was obtained from Pure Chem Chemical Co., India and deionized (D.I) water. Sodium molybdate dihydrate (Na₂MoO₄·2H₂O), 98%), Silver Nitrate ((Ag(NO₃), 98.5%), Acetone (C₃H₆O, 99%), Hydrochloric Acid (HCl, 98%) were obtained from Merck Chemical Co., India. All chemical reagents were used without any refinement.

2.1

2.1 Synthesis procedure

g-C₃N₄ nanosheets: 8 g melamine was taken in a crucible with cover and heated 540 °C into muffle furnace with 5°/min for 3 h. The yellow product of bulk g-C₃N₄ was obtained. The bulk g-C₃N₄ (1 g) was treated by a postprocessing (20 wt% of HCl in 50 mL of H₂O) for 10 h by progressing the protonation at room temperature and collected product was ultrasonically dispersed in 1 h. Finally, the obtained product was dried at 85 °C in a hot air oven for 8 h, hence the g-C₃N₄ nanosheets are got (Yao et al., 2014).

g-C₃N₄-Bi₂MoO₆-Ag nanocomposites: The preparations of the g-C₃N₄-Bi₂MoO₆ nanocomposite was through a facile hydrothermal strategy. In a typical precursor, 50 mL of ethylene glycol, 40 mL of deionized water and 30 mL of ethanol absolute were used (Sun et al., 2017). The bismuth nitrate (0.8433 g), sodium molybdate dihydrate (0.842 g), 0.5 g of gC₃N₄ nanosheets and 1.5 g of NaOH solution were added to the precursor solution and stirred for 5 h at 55 °C. With the mixed suspension was transferred by Teflon-lined stainless autoclave and kept in a hot air oven at 160 °C for 12 h. After cooling, the obtained product was washed by centrifuge through the ethanol and D.I water and dried at 100 °C for 12 h, hence they obtained product labeled as g-C₃N₄-Bi₂MoO₆ nanocomposites. In next, the attained 0.5 g of g-C₃N₄-Bi₂MoO₆ and 0.4248 g of AgNO₃ were dissolved also dispersed by ultrasonically in the 20 mL of ethylene glycol, 20 mL of ethanol combined precursors for 1 h, then the solution was mixed with stirrer for 6 h, After the stirring process the mixed suspension was further moved to Teflon-lined autoclave and kept at hot air oven at 160 °C for 12 h, Then the subsequent product was washed through centrifuge over the ethanol and D.I water for several time and finally it has dried at 70 °C for 8 h. Lastly, the gC₃N₄-Bi₂MoO₆-Ag nanocomposite was attained.

2.2

2.2 Materials characterization

The crystalline phase of the synthesized samples was tested on powder X-ray diffraction analysis through Rigaku Miniflex-II X-ray diffractometer. Surface morphology, elemental, mapping analysis and interlayer of deep morphology were characterized by high-resolution scanning electron microscopy HR-SEM (FEI Quanta FEG-200) and HR-TEM (Jeol/JEM 2100). Chemical interpretation and surface analysis of the sample was measured using XPS by ESCA 3 Mark-II Spectrometer. FT-IR spectra, UV–Vis DRS and PL spectroscopy were analyzed by Perkin Elmer, Ocean Optics USB4000, and Perkin Elmer LS45 spectrophotometers respectively. Electrochemical impedance spectroscopy (EIS) and photocurrent responses were evaluated by CHI-760 electrochemical workstation. The foremost methylene blue (MB) dye degradation measurement was done using UV–Vis Spectroscopy in Perkin Elmer Lambda 25 spectrometer. The Brunauer-Emmett-Teller (BET) of the specific surface area and pore size distributions were measured using N₂ adsorption–desorption equilibrium by Micromeritics ASAP 2020 Porosimeter. Inhibition zone calculation of antibacterial activities was designed via weld-diffusion method at room atmosphere.

2.3

2.3 Photocatalytic activities under visible light exposure

Photocatalytic activities of the prepared photocatalysts were assessed in terms of photodegradation into 30 ppm of MB aqueous dye solution (100 mL of D.I water, 50 mg of catalyst). A 500 W halogen lamp equipped with wavelength cutoff filters for λ > 400 nm was exploited. Before that, the irradiation, in suspensions were ultra-sonicated for 10 min and then mild stirring in the dark aimed at 30 min to accomplish the adsorption–desorption equilibrium formation. After revolving on the lamp, 2 mL of suspension was sampled at certain time intervals (20 min) and centrifuged at 2000 rpm for 5 min to eliminate the catalytic particles. The upper clear liquid was examined by the typical absorption peak of MB dye at 664 nm, hence to estimate the concentration dye and degradation efficiency in concurrently (Li et al., 2013).

2.4

2.4 Measurements of electrochemical impedance spectroscopy and photocurrent responses

The photo-electronic belongings of synthesized composites were measured using a electrochemical instrument with the distinctive three-electrode system. Herewith, involving the Pt wire as counter electrode, Ag/AgCl as reference electrode, sample-coated Indium Tin oxides (ITO) glass as working electrode, and chief aqueous solution of Na₂SO₄ (0.1 M) was used as electrolyte (Wang et al., 2018). Through the procedure, the applied voltage can be varied within +10 V to −10 V. When the irradiation was used in the photocurrent measurements, with Xe lamp and UV band filter remains achieved to 0.35 V vs Ag/AgCl. Hence the resulting plots were collected at various frequencies of light in ON/OFF conditions. Likewise, this functionalization will be used to measure up the chief EIS analysis.

3 Results and discussion

3.1

3.1 Structural and functional analysis

XRD patterns of synthesized g-C₃N₄, g-C₃N₄-Bi₂MoO_6, and g-C₃N₄-Bi₂MoO₆-Ag nanocomposites are exposed in Fig. 1. The peaks are indexed to the (1 0 0) and (0 0 2) diffraction planes, which are attributed to the graphitic phase of g-C₃N₄, and it will compare to standard JCPDS card data (87-1526) (Sun et al., 2017). The additional diffraction peaks of the samples are indexed by Bi₂MoO₆ (JCPDS 20–0169) and Ag (02-1067)) standard JCPDS data files. In addition, the diffraction peaks assigned to g-C₃N₄ among the three samples remained unaffected, signifying that the structure of g-C₃N₄ has not changed subsequently the loading of Bi₂MoO₆ and Ag nanomaterials also (He et al., 2018). The crystallite size was calculated by Scherrer formula, and the crystalline size is 35.3, 38 and 32 nm in the prepared g-C₃N₄, g-C₃N₄-Bi₂MoO₆ and g-C₃N₄-Bi₂MoO₆-Ag nanocomposites respectively.

FTIR spectra were further used to examine the functional groups of synthesized nanocomposites as exposed in Fig. 2. For the samples, there are occurs in a broad peak at 3000–3600 cm⁻¹ has assigned to the stretching vibration of N—H components and O—H bands. The spectra of entire samples possess the feature bands of tri-s-triazine units about 800 cm⁻¹ and C—N heterocycles among the 1600 and 1200 cm⁻¹, where it was alike to those of pristine g-C₃N₄ material (Tian et al., 2015). More importantly, the characteristic peak of Bi₂MoO₆ and Ag was found at 511 and 520 cm⁻¹ in their spectra.

3.2

3.2 Morphological, microstructure and elemental analysis

The morphologies of the prepared nanocomposites were characterized by HR-SEM observations. The HR-SEM images show that the g-C₃N₄ sample comprises a sheet-like typical structure derived from the melamine Fig. 3 a. In g-C₃N₄-Bi₂MoO₆ and g-C₃N₄-Bi₂MoO₆-Ag are also sheet-like pellets were formed Fig. 3 b and c. The g-C₃N₄-Bi₂MoO₆-Ag nanocomposite is composed well-dispersed particles whereas typical mesoporous structure, whose surface was composed by tiny spherical and ellipsoidal particles on the g-C₃N₄ layered structure (Ma et al., 2015). The gC₃N₄-Bi₂MoO₆-Ag nanocomposite contains all the elements such as C, N, Bi, Mo, O, Ag has been well agreeing as chemical composition was evaluated from EDAX, and the composition level has revealed in the table (insert Fig. 3d). The prominent X-ray elemental mapping outline of the g-C₃N₄-Bi₂MoO₆-Ag nanocomposite was shown in Fig. 4, which suggest that the C, N, Bi, Mo, O, and Ag Fig. 4 (b–g)) components are dispersed homogeneously on the ternary nanocomposites (Zhao et al., 2015).

HRSEM images of (a) g-C3N4 nanosheets, (b) g-C3N4-Bi2MoO6 and (e) g-C3N4-Bi2MoO6-Ag nanocomposites, (d) EDX spectra of g-C3N4-Bi2MoO6-Ag nanocomposites.

Elemental mapping analysis of (c) C, (d) N, (e) Bi, (f) Mo, (g) O, and (h) Ag in the g-C3N4-Bi2MoO6-Ag nanocomposites.

The insight morphologies and micro/nanostructures of synthesized nanocomposites were checked by TEM analysis. Fig. 5 (a–f) were well-disposed by the TEM images of g-C₃N₄ nanosheets, g-C₃N₄-Bi₂MoO₆ and g-C₃N₄-Bi₂MoO₆-Ag nanocomposites, which is also sheet-like morphology, whereas uniform distribution, highly dispersed particle in the average size of about 38–43 nm. The nanocrystalline showed a high crystallinity of lattice spacing (d) values around to 0.328 nm, which is in upright agreeing with the (0 0 2) lattice spacing of g-C₃N₄ nanosheets (Li, 2017). The SAED patterns are shown in Fig. 5, which was confirmed in circular fringes with dots represented by highly dispersed good crystalline nature and fine regularity of crystalline phase without any mis-arrangements (Tonda et al., 2016). From the HR-SEM and TEM images, we have seen the adjacent interface between g-C₃N₄, Bi₂MoO₆ and Ag can be originating from a close contact of Bi₂MoO₆/Ag nanocomposites with the g-C₃N₄ nanosheets. Such together the interface is valuable to the efficient migration of photogenerated electrons and holes because less of barriers existence of g-C₃N₄/Bi₂MoO₆ and g-C₃N₄/Ag heterostructures in the nanocomposites. In order to evidence the consequence of intimate interface for improving photocatalytic activity of g-C₃N₄-Bi₂MoO₆-Ag nanocomposite, mechanically mixed good combinations of novel materials in the chief sample with substantial interfaces was also enhanced in photocatalytic performances. Based on the results of HR-SEM, TEM, EDX and elemental mapping analysis established the development of ternary gC₃N₄-Bi₂MoO₆-Ag nanocomposites was a good interfacial interaction between Bi₂MoO₆, Ag nanoparticles with g-C₃N₄ nanolayered structures and the self-assembly of components were distributed uniformly.

TEM images of (a) g-C3N4 nanosheets (c) g-C3N4-Bi2MoO6 and (e) g-C3N4-Bi2MoO6-Ag nanocomposites; (b), (d) and (f) were corresponding SAED pattern.

3.3

3.3 X-ray photoelectron spectroscopy (XPS) analysis

Fig. 6 shows the XPS spectra which indicate the existence of carbon, nitrogen, bismuth, molybdenum, silver and oxygen elements in the g-C₃N₄-Bi₂MoO₆-Ag hybrid nanocomposites. C 1s XPS spectrum Fig. 6a has obviously displayed in two characteristic peaks were positioned at 284.5 and 287.8 eV (Wang et al., 2016). A wide peak around at 398.6 eV of the N 1s band spectrum Fig. 6 b is observed, which is corresponding to C-N-C coordination, by means of g-C₃N₄ composition. In the signal, Bi 4f is observed Fig. 6 c at consistent binding energies about 159.2 (Bi 4f_5/2) and 164.6 eV (Bi 4f_7/2), have been ascribed by Bi metallic compound. The distinctive spin-orbital splitting photoelectrons for Mo 3d (232.5 and 235.6 eV) has designated in a capable state for Fig. 6 d Mo atoms. In chief, such as the typical peaks of Ag 3d can be perceived Fig. 6 e, in the Ag metal ions, whereas the peaks at 367.8 and 374 eV are attributed to the Ag 3d_3/2 and Ag 3d_5/2 orbital region (Yin et al., 2017). Also, the prominent O 1s is detected in Fig. 6 f at 531.4 and 533 eV in the XPS spectrum where it is well-agreeing in the MoO₆ functionalization of g-C₃N₄-Bi₂MoO₆-Ag nanocomposites.

X-ray photoelectron spectra of g-C3N4-Bi2MoO6-Ag nanocomposites.

3.4

3.4 Optical analysis

Fig. 7 was displays the optical absorptions of prepared g-C₃N₄, g-C₃N₄-Bi₂MoO₆ and gC₃N₄-Bi₂MoO₆-Ag hybrid nanocomposites using UV-DRS spectra. By comparing with the pristine g-C₃N₄, the absorbance of hybrid samples presented in a fair enhancement of the visible region (Xu et al., 2013). The spectrum of pristine g-C₃N₄ has exposed a sharp absorption edge at UV region, however, the sample after composed with Bi₂MoO₆ and Ag nanomaterials had a minor effect on shifting in absorption edge towards the region of visible light. The g-C₃N₄ and g-C₃N₄-Bi₂MoO₆ samples have shown in an absorption edge were approximately near to 340–385 nm which are represented by Fig. 7UV-DRS spectra. In contrast, the spectra of g-C₃N₄-Bi₂MoO₆-Ag nanocomposite exhibited long absorption at ∼390 nm, while the existence of visible region which confirms the reductions of the bandgap. The optical bandgap of prepared g-C₃N₄, g-C₃N₄-Bi₂MoO_6, and g-C₃N₄-Bi₂MoO₆-Ag nanocomposites are approximately 2.7, 2.59 and 2.5 eV (insert of Fig. 7) respectively, which is calculated by Kubelka Munk functions. By means of (αhν) = A(hν − Eg)^n/2, where α, h, ν, Eg, and A are the absorption coefficient, Planck’s constant, light frequency, bandgap energy, and constant respectively. Also, the ‘n’ depends on the characteristics of the transition in a semiconductor. The power factor (n) takings the values of (0.5, 1, 1.5, 2 and 3, 4) for permitted direct, permitted indirect, forbidden direct and forbidden indirect transitions individually. For g-C₃N₄ the value of n is 4 for the indirect transition (Lin et al., 2017). In general, the direct transition is 1 and the indirect transition is 4. For Ag and Bi₂MoO₆, mutually of their n values are 1 for the direct transition. Then, the bandgap energy of g-C₃N₄ and Ag/Bi₂MoO₆ would be attained by generalizing the linear part of (αhν)² contrasted with photon energy (hν) to the x-axis. Here, the energy gap of energy transition has narrowed down and hence the transition of electrons will be easily moved due to the interaction between Ag and Bi₂MoO₆. Moreover, the g-C₃N₄-Bi₂MoO₆-Ag nanocomposite was enhanced visible light absorption property, which means the resulting in a reduction of bandgap values will be obeyed into chief behaviors in the easy separation of photogenerated charge carrier’s (Xu et al., 2013; Lin et al., 2017; Deng et al., 2018 ). Meanwhile, the Bi₂MoO₆ and Ag²⁺ metal ions have to perform as the electron scavenger could promote the segregation of electrons and holes in the entire composites. These results have designated the g-C₃N₄-Bi₂MoO₆-Ag hybrid composite can be able to absorb the more visible light and thus exhibit improved catalytic activities compared than to other prepared samples.

UV–Vis Spectra of prepared samples and (insert) Tauc Plot of bandgap measurements.

3.5

3.5 Photoluminescence analysis

To characterize the separation efficiency of photogenerated charge carriers were examined by photoluminescence (PL) spectra as exposed in Fig. 8. Prepared nanocomposites show a strong emission peak at ∼466 nm (excitation wavelength of 364 nm at room temperature). The PL intensities of the nanocomposites were significantly decreased as follows the order g-C₃N₄ > g-C₃N₄-Bi₂MoO₆ > g-C₃N₄-Bi₂MoO₆-Ag. Particularly, the g-C₃N₄-Bi₂MoO₆ and g-C₃N₄-Bi₂MoO₆-Ag nanocomposites have been exhibited on much weaker in the PL intensities than the g-C₃N₄ sample, which is indicates that the addition of Bi₂MoO₆ and Ag ions could prevent the well-known recombination of chief g-C₃N₄ charge carriers in their g-C₃N₄-Bi₂MoO₆-Ag nanocomposite (Deng et al., 2018) The PL results were evidenced in the importance of heterostructured gC₃N₄-Bi₂MoO₆-Ag nanocomposite was suitable blocking in the recombination of electrons and holes (e⁻/h⁺) pairs (An et al., 2016).

Photoluminescence spectra of as prepared samples.

3.6

3.6 Photocatalytic activity

The photocatalytic activities of the prepared photocatalyst were assessed by monitoring the decomposition of aqueous in a Methylene Blue (MB, 30 ppm) dye solution under the visible light irradiation. Fig. 9 demonstrate that the degradation of MB dye solution in the g-C₃N₄-Bi₂MoO₆-Ag photocatalytic sample, has established with the intensity of maximum absorption band positioned at 664 nm is gradually decreased with the increases of irradiation time (at regular interval of 20 min). The standardized residual concentration of MB dye was calculated using the following relationship C/Co = A_t/Ao, where C is residual concentration of MB dye, C_o is initial concentration of MB dye, A_t is intensity of absorption band after any irradiated time t and Ao is the intensity of absorption band at time t = 0. The calculated value of photodegradation as a function of irradiation time has accessible (Lu et al., 2017).

Photocatalytic activity of prepared gC3N4-Bi2MoO6-Ag nanocomposite for MB dye solution under visible irradiation at 80 min.

After adding in the catalysis, clearly, the pristine g-C₃N₄ sample shows the slight change of degradation in MB dye for 80 min under visible light irradiations. The g-C₃N₄-Bi₂MoO₆ and gC₃N₄-Bi₂MoO₆-Ag samples exhibition their ability to the high removal of the MB dye, which is displayed in Fig. 10. However, the synergistic effects can have induced in the contributions of Bi₂MoO₆ and Ag species were mixed into g-C₃N₄ to form the g-C₃N₄-Bi₂MoO₆-Ag material, hence being its photocatalytic activity was an obvious enhancement compared to g-C₃N₄-Bi₂MoO₆ and g-C₃N₄ samples. Presenting in the high photocatalytic activity may due to the following aspects: (1) improved light absorption capability; (2) action of both h⁺/e⁻ traps to decrease the recombination rate of electron and hole pairs throughout the catalytic process (Huang et al., 2018).

Degradation rate of the MB solution by prepared nanocomposites.

Fig. 10 displays the photocatalytic key kinetics (C/Co) over the different photocatalysts. In the g-C₃N₄ nanosheet, the sample was only reduced to the concentration of MB dye, which is optimum of 45% after 80 min of visible-light irradiation (Zhang et al., 2017). Whereas the Bi₂MoO₆ contained g-C₃N₄ catalyst show higher photocatalytic activity, with the degradation of 73% in the equal time interval. In ternary, the gC₃N₄-Bi₂MoO₆-Ag nanocomposite exhibited remarkably enhanced photocatalytic activity, in which the concentration of MB is reduced by around 99.6% at the similar exposure time. The excellent photocatalytic behavior caused by the interlayer of chief Ag nanoparticles which is participating in the charge transfer and bridge of bandgap (Cui et al., 2017) between the gC₃N₄ and Bi₂MoO₆. Hence, this precise effort was primarily due to the visible light absorption capacity and synergistic effect exists whereas, enabling the separation of photoexcited charge carrier’s and dropping the recombination of the photogenerated electron-hole pairs.

The quantitative investigation of the reaction kinetics of MB dye photodegradation by the prepared photocatalysts was also performed in Fig. 11. The tentative data were fitted by the pseudo-first-order kinetics in typical model of ln(C₀/C) = Kt, where the value of the reaction rate constant K is equal to the corresponding slope of the fitting line (Reda et al., 2020). Linear relationships were attained as represented which indicating that the MB photodegradation process can be fitted by the pseudo-first-order model. As shown in Fig. 11, the g-C₃N₄-Bi₂MoO₆-Ag catalyst has the highest degradation rate constant K_MB (0.3463 min⁻¹), about 2.1 and 3.6 times higher than pristine g-C₃N₄ and g-C₃N₄-Bi₂MoO₆ respectively. In short, the g-C₃N₄-Bi₂MoO₆-Ag catalyst exhibits a dramatic development in photocatalytic activity compared to g-C₃N₄ and g-C₃N₄-Bi₂MoO₆ under identical circumstances (Vignesh and Sundar, 2018).

Kinetics in MB dye degradation of prepared photocatalysts.

3.7

3.7 Recycle stability for practical applications

The reusability of the photocatalyst was topmost aspects for practical applications which is probable of long-term usability in the chief photocatalysts (Huang et al., 2018). Moreover, we attempt favorable reagent, by means, the g-C₃N₄-Bi₂MoO₆-Ag photocatalyst for the treatment in similar 30 ppm of identical MB dye has been studied up to 5 cycles for ∼7 h. As shown in Fig. 12, the g-C₃N₄-Bi₂MoO₆-Ag nanocomposite displays in superior photocatalytic activity and around 99.6 to 96% of MB dye can be degraded into 5 successive cycles. After the five cycles, the photocatalytic activities of chief g-C₃N₄-Bi₂MoO₆-Ag catalyst was only decreased 3% only up to 5 cycles, hence it's perhaps due to the loss of photocatalyst through recycling or some intermediates covered in the surface of photocatalyst (Wang et al., 2017). In their stability of samples was checked out in the XRD and FTIR analysis and it will no chief structural and functional defects (Mitra et al., 2016) can be occurring after the five cycles, hence its shown in Fig. 13 (a) and (b). Since the above results can conclude the obtained functional groups of nanocomposites can comprise the catalytic process but do not the loss of any other structural and functional factors. In the g-C₃N₄-Bi₂MoO₆-Ag nanocomposite has been outstanding photocatalyst also displays a stable catalytic activity after the 5 successive cycles.

Cycling runs for the photocatalytic degradation of MB over gC3N4-Bi2MoO6-Ag nanocomposites under visible light irradiation.

(a) XRD and (b) FTIR spectra of after photocatalytic processed samples.

3.8

3.8 BET analysis (Surface areas and porosity)

The Brunauer-Emmett-Teller (BET) technique was used to measure the specific surface area and pore size distributions of prepared nanocomposites by N₂ adsorption–desorption equilibrium conditions as shown in Fig. 14 (Vadivel et al., 2018). The BET analysis results exposed the surface area was observed at 42.3 cm³ g⁻¹, 62.6 cm³ g⁻¹ and 97.4 cm³ g⁻¹ for g-C₃N₄, g-C₃N₄-Bi₂MoO₆ and gC₃N₄-Bi₂MoO₆-Ag nanocomposites respectively. The large surface area of g-C₃N₄-Bi₂MoO₆-Ag photocatalyst has indicated that the reductions of recombination rate of photogenerated charge carriers. Moreover, the expanded pore volume and diameter, whereas improved separation and migration of photogenerated charges, since it leads to being enhanced the photocatalytic activities. Hence, the above results, the chief gC₃N₄-Bi₂MoO₆-Ag composite is useful for the better adsorption and also delivers a higher number of reactive sites for photocatalytic progression, whereas, the significant influence to the improvement of photocatalytic efficiency (Papailias et al., 2017; Sharma et al., 2017). Importantly, along with the apparent increment in surface area, an increase in the pore volume (insert of Fig. 14) from 0.13 cm³ g⁻¹ for prepared g-C₃N₄ to 0.42 cm³ g⁻¹ for gC₃N₄-Bi₂MoO₆-Ag was observed, which facilitated the charge separation in the entire composite system. Also, the pore diameter from 10.1 nm for prepared g-C₃N₄ to 14.6 nm for g-C₃N₄-Bi₂MoO₆-Ag was observed owing to the additions of effective Ag and Bi₂MoO₆ components. Some important parameters of the prepared nanocomposites are recorded in Table 1.

N2 Adsorption - desorption isotherms and the corresponding (insert) pore-size distribution curves for as prepared nanocomposites.

Table 1 Significant parameters of synthesized nanocomposites.

Samples	Crystallite size (nm)	Bandgap (eV)	Degradation%	First order kinetics (R²)	BET surface area (cm³/g)
g-C₃N₄	35.3	2.7	45	0.9031	42.3
g-C₃N₄-Bi₂MoO₆	38	2.59	73	0.9192	62.6
g-C₃N₄-Bi₂MoO₆-Ag	32	2.5	99.6	0.9474	97.4

3.8.1

3.8.1 Trapping mechanism

To further investigate the photocatalytic mechanism of the chief g-C₃N₄-Bi₂MoO₆-Ag nanocomposite were using into BQ, IPA and TEOA through evaluated with the scavengers of O₂^•−, OH^• and holes (h⁺) radicals, respectively. When 0.5 mM of BQ was added to the MB dye solution in the existence of gC₃N₄-Bi₂MoO₆-Ag photocatalyst, the degradation rate was decreased as 30%, which infer that the kind active species of h⁺ radical is tiniest affect only (Huang et al., 2016). While the degradation rate of MB dye remains decreased by the addition of TEOA, hence signifying that the O₂^•− radical has played a certain role in the existing photocatalysis process. When IPA was added, then the degradation rate of MB dye was highly affected due to the representing that OH^• radical was completely arrested at the same time, the present mechanism has discovered, hence could not able to harvest OH^• radicals (Zhou et al., 2017). So, the photocatalytic degradation efficiency drastically decreased (81%) compared to them without scavengers as to be clear from Fig. 15. In other words, due to the mechanism will simply explain for the photogenerated (e⁻-h⁺) pairs are separated and participate to form superoxide radical anions (O₂^•−) and hydroxyl radicals (OH^•−) which are significant oxidative species to degrade the MB dye into harmless H₂O and CO₂ (Kumar et al., 2014). The evolution of photocatalytic activities over the g-C₃N₄-Bi₂MoO₆-Ag nanocomposites has generally described according to the probable mechanism has illustrated in the following Eqs. (1)-(5).

(1)

g-C₃N₄ − Bi₂MoO₆ − Ag + hν →g-C₃N₄ − Bi₂MoO₆ − Ag + (e⁻(CB) + h⁺(VB)) →

(2)

OH + MB → CO₂ + H₂O →

(3)

h⁺ + MB → CO₂ + H₂O →

(4)

H₂O + h⁺ → OH^•/H⁺ →

(5)

OH^•−/h⁺ + MB → degradation products + CO₂ + H₂O →

Effects of different scavengers on the degradation of MB dye in presence of g-C3N4-Bi2MoO6-Ag nanocomposites.

3.9

3.9 Possible mechanism of the enhanced photocatalytic activity

Based on above results, the practical photodegradation mechanism of the g-C₃N₄-Bi₂MoO₆-Ag nanocomposite was revealed and thus proposed and schematically exhibited in graphical abstract. When the light illuminates into g-C₃N₄-Bi₂MoO₆-Ag nanocomposite, the photons have highly disturbing will possessing energies equal to or higher than the bandgap energies of Bi, Mo, and Ag contents can have a generation of excited positive holes in the valence band and electrons in the conduction band. Bi₂MoO₆ and Ag have led to the narrowing the bandgap, so it becomes easier to separate the photoinduced charges under the visible light irradiation (Zeng et al., 2016), which assists as both the electron acceptor and donor, will succeed in conquering the electrons-holes recombination and construction a more active species to endorse the degradation of MB dye. Hence, the Bi₂MoO₆ and Ag are a great impurity in the process of reducing the bandgap of the g-C₃N₄ nanomaterials. That impurity can reduce the energy of the electronic level from VB to CB which is owing to the recombination rate of electron-hole pairs (Babu et al., 2018). The high removal of the photoelectron can constrain in the recombination of photoinduced charges and their motivated photocatalytic activities. It is mentioned graphically to the probable mechanism in Fig. 18. Moreover, the photocatalytic activities of the prepared g-C₃N₄-Bi₂MoO₆-Ag nanocomposite were compared to previously reported under the visible light irradiation of various metal oxides and other nanocomposites as revealed in Table 2. From the Table, it is clear that the g-C₃N₄-Bi₂MoO₆-Ag nanocomposite materials have shown to improved visible-light-induced photocatalytic activity compared to reported composites (Babu et al., 2018; Priyadharsan et al., 2017; Si et al., 2018; Rashad et al., 2014; Wang et al., 2016; Mohammadi et al., 2016; Yousefi et al., 2015; Leelavathi et al., 2013; Nagaraju et al., 2017; Yao et al., 2014; Sanoop et al., 2016; Chen et al., 2014 ).

Table 2 Comparison of visible light generated MB degradation rate (%) over previously reported metal oxides and associated to the g-C₃N₄ catalysts.

S. No	Catalyst		Irradiation time (mins)	Degradation efficiency (%)	References
1.	g-C₃N₄ -SnO₂ QDs	50 mg	180	94	Babu et al. (2018)
2.	CeO₂/SnO₂/rGO	50 mg	90	90	Priyadharsan et al. (2017)
3.	TiO₂	50 mg	120	90	Si et al. (2018)
4.	ZnO-SnO₂	100 mg	240	91	Rashad et al. (2014)
5.	g-C₃N₄-MoS₂-Fe	60 mg	150	99	Wang et al. (2016)
6.	TiO₂/ZnO/CuO	150 mg	120	62	Mohammadi et al. (2016)
7.	Sr: ZnO	100 mg	120	98	Yousefi et al. (2015)
8.	PbO/TiO₂	100 mg	120	78	Leelavathi et al. (2013)
9.	Ag/ZnO	200 mg	150	98	Nagaraju et al. (2017)
10	g-C₃N₄-ZnFe₂O₄	50 mg	240	97	Yao et al. (2014)
11.	rGO/ZnO	20 mg	90	99	Sanoop et al. (2016)
12.	g-C₃N₄-Ag-TiO2	135 mg	300	99	Chen et al. (2014)
13.	g-C₃N₄-Bi₂MoO₆-Ag	50 mg	80	99.6	This work

On the substance of above discussion, a schematic illustration of the photodegradation phenomenon was depicted in graphical abstract. The electron and holes were a generation in the CB and VB are shown to be strongly related to Mullikan electronegativity theory whereas used to compute the CB and VB potential values (Nagaraju et al., 2017). The following expressions are used to calculate the corresponding potentials.

(6)

E_{VB} = X - E_{e} + 0.5 E_{g} \to

(7)

E_{CB} = E_{VB} - E_{g} \to

where E_VB and E_CB are potentials of the valence and conduction bands, respectively. In major function of X is absolute electronegativity of the semiconductor ∼ (X = 4.72, 5.55, 1.93 eV for g-C₃N₄, Bi₂MoO_6, and Ag materials) and Ee is the hydrogen scale values of free electron energy which is 4.5 eV (Nagaraju et al., 2017). In the prepared the pristine g-C₃N₄; Bi₂MoO₆ and Ag bandgap are 2.7, 2.45, 1.69 eV respectively. X is obtained by taking the arithmetic mean of first ionization energy and electron affinity of the constituent atoms. Hence the calculated potentials of the VB and CB are (g-C₃N₄: 1.57 and −1.13 eV; Bi₂MoO₆: 2.27 and −0.17 eV; Ag: −1.72 and −3.41 eV) described by above equations. These results are less than similar to the earlier reports (Yao et al., 2014; Sanoop et al., 2016; Chen et al., 2014 ). The band gap is reduced due to Ag loading in g-C₃N₄-Bi₂MoO₆. Since the Ag ions could replace the Bi and MoO₄⁺ ions at their donor impurity levels are formed by means of conduction band for g-C₃N₄ nanomaterials, and hence, the band gap is also reduced also the catalytic activity should enhance compatible.

3.10

3.10 Electrochemical impedance spectroscopy

Additionally, the electrochemical measurements of the EIS and photocurrent responses were measured to investigate the charge transfer resistance with a separation efficiency of photoinduced charge carriers (e⁻-h⁺) (Bao and Chen, 2017). Fig. 16 (a) shows that the EIS Nyquist plots of synthesized nanocomposites. From the result, they have moderately to decreased the EIS radius was revealed for the representative g-C₃N₄-Bi₂MoO₆-Ag nanocomposite has compared with g-C₃N₄, g-C₃N₄-Bi₂MoO₆ nanocomposites. Hence, they indicated that the lesser charge transfer resistance reduced electronic impedance and improved charge carrier mobility. In further, the photocurrent responses of all samples were explored in numerous on–off cycles in the mediated by visible light irradiation Fig. 16 (b)). When the light is switched on, the photocurrent responses of the employed electrodes are suddenly increased owing to the fast separation of the photogenerated charge carriers. The divergent, when the light is turned off, the photocurrent is identical less and preserves its dark in existing state. It is recognized that the attained photocurrent intensity of g-C₃N₄-Bi₂MoO₆-Ag nanocomposites has abundant development than remaining samples, which is a good agreement for reached in the more charge carrier's ability and development of photocatalytic properties (Moura et al., 2018). The photocurrent response of chief g-C₃N₄-Bi₂MoO₆-Ag nanocomposite will reach almost 3.1 times greater compared than g-C₃N₄ nanosheets. These results were indicated that the g-C₃N₄-Bi₂MoO₆-Ag catalyst could confirm that the excellent photoinduced charges can be separated and faster transferred caused by the admired effect among the Bi₂MoO₆ and Ag materials as a well-known charge carrier function of g-C₃N₄. Hence, they have inhibited the electron-hole recombination, whereas beneficial to the enhanced photocatalytic pathway (Bao and Chen, 2017; Moura et al., 2018; Singh et al., 2019 ). The PL spectra outcomes could suggestion the importance of the heterostructure of g-C₃N₄-Bi₂MoO₆-Ag in blocking the electrons and holes recombination.

(a) EIS Nyquist plot. (b) Photocurrent responses of prepared samples.

3.11

3.11 Antibacterial properties

The antibacterial properties were assessed by against E-coli (G⁺) and S-aureus (G⁻) of the differently prepared samples via the weld-diffusion process. In Fig. 17 shows the zone of inhibition (ZOI) evaluation using g-C₃N₄-Bi₂MoO₆-Ag catalytic materials against the both two bacteria’s by measuring a clear area around the samples. The g-C₃N₄ did not show any measurable clear area around the sample, suggesting negligible antibacterial properties (Adhikari et al., 2016). The clear area (ZOIs) obtained around the samples followed the order of g-C₃N₄-Bi₂MoO₆-Ag > g-C₃N₄-Bi₂MoO₆ > g-C₃N₄ nanocomposites. Because of, the reactive oxygen species has involved in their probability, hence some species are directly elaborate into destroying the outer coated area of the bacteria cell walls causing in a serious damage to the microorganism (Adhikari et al., 2016). Moreover, the microorganism which is abundant carries a negative charge while the metal oxide carries a positive charge, and this causes an electromagnetic attraction among the metal oxide and the microorganism that leads to oxidative kinetic and finally microorganism will be death. Therefore, the attachment of Bi₂MoO₆-Ag porous materials on the surface of g-C₃N₄ nanosheets will reduce the possibility of recombination, which primes to an enhancement of the antibacterial activities (Wang et al., 2017). The enhanced antibacterial activity of g-C₃N₄-Bi₂MoO₆ and g-C₃N₄-Bi₂MoO₆-Ag is directly related to the Bi₂MoO₆ also Ag nanoparticles were effectively decorated on the bacterial cell membranes.

Zone inhibition test for g-C3N4-Bi2MoO6-Ag nanocomposite towards E-coli and S. aureus bacteria’s.

The plausible mechanism of the MB dye degradation for g-C3N4-Bi2MoO6-Ag catalyst whereas the photon (hν) designates the discrete transition from CB to VB by g-C3N4, Bi2MoO6 and Ag ions, also the mechanism of bacteria’s demise.

The antibacterial activity of given nanocomposites may have ascribed to the two feasible mechanisms that means, (i) the generation of enhances stages of reactive oxygen species (ROS) i.e. corresponds of superoxide anion radicals (O₂^•−), hydroxyl radical (OH^•−) and hydrogen peroxide (H₂O₂), in next (ii) the deposition of nanomaterials on surface of the bacteria. The decreased crystallite size of the g-C₃N₄-Bi₂MoO₆-Ag nanocomposite (as confirmed by XRD analyses) is also one kind of the key reasons for enhanced bacterial exploit. Besides, the bacterial activity of the prepared catalyst can be defined as given as follows, the g-C₃N₄-Bi₂MoO₆-Ag nanocomposites with crystal defects such as typical vacancies can be triggered by both visible and UV light which means enhances wide absorption region were induced (Ma et al., 2015). When a photon has suitable energy cascades on g-C₃N₄ an electron from the VB is excited to the CB exit of holes in the VB. The enhanced electrons in the CB reacted with the softened oxygen molecules were originating into superoxide anion radicals (O₂^•−). Detailed of probable solution which may hole in the VB divided water molecule into OH and H⁺ ions. The superoxide anion radical (O₂^•−) has further reacted with the H⁺ generating OH^•− radicals. The OH^•− radical replies with electron and H⁺ yielding to the H₂O₂ molecule. Commonly the H₂O₂ can fluently penetrate to the cell membrane and eventually cause by the death of bacteria. While the g-C₃N₄-Bi₂MoO₆-Ag composites is a well-known material used for this application and are better antibacterial agent towards pathogenic bacteria’s may owing to the progress of reactive oxygen species (key kinetics of ROS) (Wang et al., 2017; Adhikari et al., 2015). Regards, the chief prospects have mentioned in graphically through the Fig. 18. Hence, the above suggestions the g-C₃N₄-Bi₂MoO₆-Ag nanocomposites can penetrate and easily disturb the bacterial cell walls. In chief, the g-C₃N₄-Bi₂MoO₆-Ag sample has much better antibacterial activity compared to g-C₃N₄ and g-C₃N₄-Bi₂MoO₆ samples, with their consistent zone of inhibition, are tabularized in Table 3.

Table 3 Evaluation on zone of inhibition of antibacterial activity for synthesized nanocomposites.

Microorganisms	Zone of inhibition range (mm)
Microorganisms	E. Coli				S. aureus
Synthesized nano-antibacterial	100 µg	150 µg	200 µg	250 µg	100 µg	150 µg	200 µg	250 µg
g-C₃N₄	10 ± 0.0	11 ± 0.5	13 ± 0.5	13 ± 0.5	10 ± 0.5	9 ± 0.5	10 ± 1	10 ± 0.5
g-C₃N₄-Bi₂MoO₆	12 ± 0.5	11 ± 0.5	12 ± 0.5	15 ± 1	10 ± 0.5	11 ± 1	13 ± 0.0	13 ± 0.5
g-C₃N₄-Bi₂MoO₆-Ag	17 ± 0.5	18 ± 1	20 ± 0	18 ± 0.5	16 ± 0.5	17 ± 0.5	19 ± 1.0	19 ± 0.5

4 Conclusion

In summary, a ternary Bi₂MoO₆-Ag composed g-C₃N₄ layered structure was successfully synthesized by a facile approach and the excellent photocatalytic activity could be exhibited. Consistently, the g-C₃N₄-Bi₂MoO₆-Ag composites have synergistically facilitated the photocatalysis process was due to the interfacial effects of beneficial for the separation of photogenerated charge carriers, be means lower bandgap range, highly accessible reactive sites and high surface area. Compared with the pristine g-C₃N₄ and g-C₃N₄-Bi₂MoO₆, the photodegradation ability of the MB dye toward the g-C₃N₄-Bi₂MoO₆-Ag catalyst under the visible light irradiation is considerably enhanced, wherein 99.6% can be removed for 80 min, hence the Bi₂MoO₆ and Ag via the improvement of interfacial connections with visible light harvesting ability. The chief g-C₃N₄-Bi₂MoO₆-Ag catalyst could support a long-term application of g-C₃N₄-Bi₂MoO₆-Ag in water treatment even after the five successive cycles and without loss. Owing to the scavenger’s test, the superoxide radical O₂^•− and hydroxyl radical (OH^•−) plays a significant role in dye degradation process. The photocurrent responses exposed that the g-C₃N₄-Bi₂MoO₆-Ag catalytic system where good carrier transport, and more active electron-hole separation process. The g-C₃N₄-Bi₂MoO₆-Ag nanocomposite has possessed a superior antibacterial effect in both G⁺ and G⁻ bacterial strains. The findings in this effort can deliver a good case for the schema of effectual, visible light driven, and reusable photocatalyst for environmental remediation of the organic pollutants.

Acknowledgement

The authors thanks the UGC for providing the fund through BSR Scheme.

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Appendix A

Supplementary material

Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.arabjc.2018.05.009.

Appendix A

Supplementary material

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[31] Ong W.J., Tan L.L., Ng Y.H., . Graphitic carbon nitride (g-C₃N₄)-based photocatalysts for artificial photosynthesis and environmental remediation: are We a step closer to achieving sustainability. Chem. Rev.. 2016;116:7159-7329.
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[32] Papailias I., Todorova N., Giannakopoulou T., . Photocatalytic activity of modified g-C₃N₄/TiO₂ nanocomposites for NOx removal. Catal. Today. 2017;280:37-44.
[Google Scholar]

[33] Priyadharsan A., Vasanthakumar V., Karthikeyan S., Raj V., Shanavas S., Anbarasan P.M., . Multi-functional properties of ternary CeO₂/SnO₂/rGO nanocomposites: visible light driven photocatalyst and heavy metal removal. J. Photochem. Photobiol. A Chem.. 2017;346:32-45.
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[34] Rashad M.M., Ismail A.A., Kandil A.T., Osama I., Ibrahim I.A., . Photocatalytic decomposition of dyes using ZnO doped SnO₂ nanoparticles prepared by solvothermal method. Arab. J. Chem.. 2014;7:71-77.
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[35] Reda S.M., Khairy M.A., Mousa M.A., . Photocatalytic activity of nitrogen and copper doped TiO₂ nanoparticles prepared by microwave-assisted sol-gel process. J. Chem. Arab. 2020;13(1):86-95.
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[36] Reli M., Huo P., Šihor M., . Novel TiO₂/gC₃N₄ photocatalysts for photocatalytic reduction of CO₂ and for photocatalytic decomposition of N₂O. J. Phys. Chem. A. 2016;120:8564-8573.
[Google Scholar]

[37] Sanoop P.K., Anas S., Ananthakumar S., Gunasekar V., Saravanan R., Ponnusami V., . Synthesis of yttrium doped nanocrystalline ZnO and its photocatalytic activity in methylene blue degradation. J. Chem Arab. 2016;9(S2):S1618-S1626.
[CrossRef] [Google Scholar]

[38] Sharma M., Vaidya S., Ganguli A.K., . Enhanced photocatalytic activity of g-C₃N₄/TiO₂ nanocomposites for degradation of Rhodamine B dye. J. Photochem. Photobiol. A Chem.. 2017;335:287-293.
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[39] Si Y., Liu huanhuan, Li N., Zhong J., Li J., Ma D., . SDBS-assisted hydrothermal treatment of TiO₂ with improved photocatalytic activity. Mater. Lett.. 2018;212:147-150.
[Google Scholar]

[40] Singh P., Priya B., Shandilya P., Raizada P., Singh N., Pare B., Jonnalagadda S.B., . Photocatalytic mineralization of antibiotics using 60% WO₃/BiOCl stacked to graphene sand composite and chitosan. J. Chem. Arab.. 2019;12(8):4627-4645.
[CrossRef] [Google Scholar]

[41] Sun L., Du T., Hu C., . Antibacterial activity of graphene oxide/g-C₃N₄ composite through photocatalytic disinfection under visible light. ACS Sustain. Chem. Eng.. 2017;5:8693-8701.
[Google Scholar]

[42] Tian J., Hao P., Wei N., Cui H., Liu H., . 3D Bi₂MoO₆ nanosheet/TiO₂ nanobelt heterostructure: enhanced photocatalytic activities and photoelectochemistry performance. ACS Catal.. 2015;5:4530-4536.
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[43] Tonda S., Kumar S., Shanker V., . Surface plasmon resonance-induced photocatalysis by Au nanoparticles decorated mesoporous g-C₃N₄ nanosheets under direct sunlight irradiation. Mater. Res. Bull.. 2016;75:51-58.
[CrossRef] [Google Scholar]

[44] Vadivel S., Muppidathi A.L., Jeyaperumal K.S., Selvaraj A., . Synthesis and characterization of multifunctional homochiral 1[HYPHEN]D aminoacetic acid potassium metal organic framework. J. Organomet. Chem.. 2018;866:206-213.
[CrossRef] [Google Scholar]

[45] Vignesh S., Lakshmi A., Jeyaperumal M., Sundar K., . nanocomposites for magnetic separable photocatalytic and antibacterial activity. J. Mater. Sci. Mater. Electron.. 2018;29:10784-10801.
[CrossRef] [Google Scholar]

[46] Vignesh Shanmugam, Sundar Jeyaperumal Kalyana, . Investigations of visible light driven Sn and Cu doped ZnO hybrid nanoparticles for photocatalytic performance and antibacterial activity. Appl. Surf. Sci.. 2018;449:617-630.
[CrossRef] [Google Scholar]

[47] Wang W., An T., Li G., Xia D., Zhao H., Yu J.C., Wong P.K., . Earth-abundant Ni₂P/g-C₃N₄ lamellar nanohydrids for enhanced photocatalytic hydrogen evolution and bacterial inactivation under visible light irradiation. Appl. Catal. B Environ.. 2017;217:570-580.
[CrossRef] [Google Scholar]

[48] Wang H., He W., Dong X., Wang H., Dong F., . In situ FT-IR investigation on the reaction mechanism of visible light photocatalytic NO oxidation with defective g-C3N4. Sci. Bull.. 2018;63:117-125.
[CrossRef] [Google Scholar]

[49] Wang X., Hong M., Zhang F., . Recyclable nanoscale zero valent iron doped g-C₃N₄/MoS₂ for efficient photocatalysis of RhB and Cr(VI) driven by visible light. ACS Sustain. Chem. Eng.. 2016;4:4055-4063.
[CrossRef] [Google Scholar]

[50] Wang D., Shen H., Guo L., Fu F., Liang Y., . Design and construction of the sandwich-like Z-scheme multicomponent CdS/Ag/Bi₂MoO₆ heterostructure with enhanced photocatalytic performance in RhB photodegradation. New J. Chem.. 2016;40:8614-8624.
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[51] Wang J., Tang L., Zeng G., . Plasmonic Bi metal deposition and g-C₃N₄ coating on Bi₂WO₆ microspheres for efficient visible-light photocatalysis. ACS Sustain. Chem. Eng.. 2017;5:1062-1072.
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[52] Xu M., Han L., Dong S., . Facile fabrication of highly efficient g-C₃N₄/Ag₂O heterostructured photocatalysts with enhanced visible-light photocatalytic activity. ACS Appl. Mater. Interfaces. 2013;5:12533-12540.
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[54] Yao Y., Cai Y., Lu F., Qin J., Wei F., Xu C., Wang S., . Magnetic ZnFe₂O₄-C₃N₄ hybrid for photocatalytic degradation of aqueous organic pollutants by visible light. Ind. Eng. Chem. Res.. 2014;53:17294-17302.
[Google Scholar]

[55] Yin M., Jia F., Wu C., . Coupling g-C₃N₄ nanobelts and Cu(OH)₂ nanoparticles with TiO₂ for visible-light photocatalytic H₂ production. Mater. Sci. Eng. B. 2017;223:35-42.
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[56] Yousefi R., Jamali-Sheini F., Cheraghizade M., Khosravi-Gandomani S., Sáaedi A., Huang N.M., Basirun W.J., Azarang M., . Enhanced visible-light photocatalytic activity of strontium-doped zinc oxide nanoparticles. Mater. Sci. Semicond. Process.. 2015;32:152-159.
[Google Scholar]

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Construction of high efficient g-C3N4 nanosheets combined with Bi2MoO6-Ag photocatalysts for visible-light-driven photocatalytic activity and inactivation of bacterias

Abstract

Keywords

gC3N4-Bi2MoO6-Ag

Nanosheets

Visible light

Degradation

Light-harvesting

High surface area

1 Introduction

2 Experimental procedure

2.1 Synthesis procedure

2.2 Materials characterization

2.3 Photocatalytic activities under visible light exposure

2.4 Measurements of electrochemical impedance spectroscopy and photocurrent responses

3 Results and discussion

3.1 Structural and functional analysis

3.2 Morphological, microstructure and elemental analysis

3.3 X-ray photoelectron spectroscopy (XPS) analysis

3.4 Optical analysis

3.5 Photoluminescence analysis

3.6 Photocatalytic activity

3.7 Recycle stability for practical applications

3.8 BET analysis (Surface areas and porosity)

3.8.1 Trapping mechanism

3.9 Possible mechanism of the enhanced photocatalytic activity

3.10 Electrochemical impedance spectroscopy

3.11 Antibacterial properties

4 Conclusion

Acknowledgement

References

Appendix A

Supplementary material

Appendix A

Supplementary material

Supplementary data 1

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Construction of high efficient g-C₃N₄ nanosheets combined with Bi₂MoO₆-Ag photocatalysts for visible-light-driven photocatalytic activity and inactivation of bacterias