An efficient Z-scheme CdS/g-C3N4 nano catalyst in methyl orange photodegradation: Focus on the scavenging agent and mechanism

Unveiling the photocatalytic potential of graphitic carbon nitride (g-C3N4): a state-of-the-art review

Graphitic carbon nitride (g-C3N4)-based materials have emerged as promising photocatalysts due to their unique band structure, excellent stability, and environmental friendliness. This review provides a comprehensive and in-depth analysis of the current state of research on g-C3N4-based photocatalysts. The review summarizes several strategies to improve the photocatalytic performance of pristine g-C3N4, e.g., by creating heterojunctions, doping with non-metallic and metallic materials, co-catalyst loading, tuning catalyst morphology, metal deposition, and nitrogen-defect engineering. The review also highlights the various characterization techniques employed to elucidate the structural and physicochemical features of g-C3N4-based catalysts, as well as their applications of in photocatalytic degradation and hydrogen production, emphasizing their remarkable performance in pollutants' removal and clean energy generation. Furthermore, this review article investigates the effect of operational parameters on the catalytic activity and efficiency of g-C3N4-based catalysts, shedding light on the key factors that influence their performance. The review also provides insights into the photocatalytic pathways and reaction mechanisms involving g-C3N4 based photocatalysts. The review also identifies the research gaps and challenges in the field and presents prospects for the development and utilization of g-C3N4-based photocatalysts. Overall, this comprehensive review provides valuable insights into the synthesis, characterization, applications, and prospects of g-C3N4-based photocatalysts, offering guidance for future research and technological advancements in this rapidly growing field.

An Efficient p-n Heterojunction Copper Tin Sulfide/g-C3N4 Nanocomposite for Methyl Orange Photodegradation

The discharge of toxic dye effluents from industry is a major concern for environmental pollution and toxicity. These toxic dyes can be efficiently removed from waste streams using a photocatalysis process involving visible light. Due to its simple synthesis procedure, inexpensive precursor, and robust stability, graphitic carbon nitride (g-C3N4, or CN) has been used as a visible light responsive catalyst for the degradation of dyes with mediocre performance because it is limited by its low visible light harvesting capability due to its wide bandgap and fast carrier recombination rate. To overcome these limitations and enhance the performance of g-C3N4, it was coupled with a narrow bandgap copper tin sulfide (CTS) semiconductor to form a p-n heterojunction. CTS and g-C3N4 were selected due to their good stability, low toxicity, ease of synthesis, layered sheet/plate-like morphology, and relatively abundant precursors. Accordingly, a series of copper tin sulfide/graphitic carbon nitride nanocomposites (CTS/g-C3N4) with varying CTS contents were successfully synthesized via a simple two-step process involving thermal pyrolysis and coprecipitation for visible-light-induced photocatalytic degradation of methyl orange (MO) dye. The photocatalytic activity results showed that the 50%(wt/wt) CTS/g-C3N4 composite displayed a remarkable degradation efficiency of 95.6% for MO dye under visible light illumination for 120 min, which is higher than that of either pristine CTS or g-C3N4. The improved performance is attributed to the extended light absorption range (due to the optimized bandgap), effective suppression of photoinduced electron-hole recombination, and improved charge transfer that arose from the formation of a p-n heterojunction, as evidenced by electrochemical impedance spectroscopy (EIS), photocurrent, and photoluminescence results. Moreover, the results of the reusability study showed that the composite has excellent stability, indicating its potential for the degradation of MO and other toxic organic dyes from waste streams.

Development of a novel Z-scheme CoxNi1-xTiO3/CdS (x = 0.5) photocatalyst for the efficient degradation of organic pollutants via a visible-light-driven photocatalytic process

Herein, for the first time, we reported the synthesis of a novel Z-scheme CoxNi1-xTiO3/CdS (x = 0.5) heterojunction photocatalyst and the investigation of its visible-light-driven photocatalytic performance toward degradation of methylene blue (MB). The developed photocatalyst was structurally characterized by applying X-Ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), differential reflectance spectroscopy (DRS), and photoluminescence (PL) techniques. The results indicated the formation of a highly porous structure with improved visible light adsorption capacity, favorable for the catalytic activity. At an optimum condition of 10 mg/L of MB and 300 mg/L of catalyst, the ternary photocatalyst demonstrated a MB removal efficiency of 99 % after 75 min of the treatment process. The radical trapping experiments unveiled that hydroxyl and superoxide radicals were two main reactive species formed under visible light, while the valance holes possessed an insignificant role. The synergetic impact of the CoxNi1-xTiO3 (x = 0.5) and CdS on the photodegradation of MB over the as-prepared CoxNi1-xTiO3/CdS (x = 0.5) photocatalyst through Z-scheme photocatalysis was indicated by the results of the mechanism studies. The percentage impact of the treatment time, MB concentration, the ratio of CoxNi1-xTiO3/CdS (x = 0.5), and the dosage of catalyst using analysis of the CCD modeling was obtained as 47.04, 16.67, 7.22 and 0.87 %, respectively. Furthermore, the as-synthesized photocatalyst possessed high recyclability and photostability with only a 3 % decline in activity after four repetitive cycles.

A facile two-step hydrothermal preparation of 2D/2D heterostructure of Bi2WO6/WS2 for the efficient photodegradation of methylene blue under sunlight

A facile two-step hydrothermal method was successfully used to prepare a photocatalyst Bi2WO6/WS2 heterojunction for methyl blue (MB) photodegradation. Fabricated photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). Band gap measurements were carried out by diffuse reflectance spectroscopy (DRS). Results indicated that the prepared heterostructure photocatalyst has increased visible light absorption. Photocatalytic performance was evaluated under sunlight irradiation for methylene blue (MB) degradation as a model dye. Variations in pH (4-10), amount of catalyst (0.025-0.1 g/L), and initial MB concentrations (5-20 ppm) were carried out, whereas all prepared catalysts were used to conduct the tests with a visible spectrophotometer. Degradation activity improved with the pH increase; the optimum pH was approximately 8. Catalyst concentration is directly related to degradation efficiency and reached 93.56% with 0.075 g of the catalyst. Among tested catalysts, 0.01 Bi2WO6/WS2 has exhibited the highest activity and a degradation efficiency of 99.0% in 40 min (min) for MB. MB photodegradation follows pseudo-first-order kinetics, and obtained values of kapp were 0.0482 min-1, 0.0337 min-1, 0.0205 min-1, and 0.0087 min-1 for initial concentrations of 5 ppm, 10 ppm, 15 ppm, and 20 ppm, respectively. The catalyst was reused for six cycles with a negligible decrease in the degradation activity. Heterostructure 0.01 Bi2WO6/WS2 has exhibited a photocurrent density of 16 μA cm-2, significantly higher than 2.0 and 4.5 μA cm-2 for the pristine WS2 and Bi2WO6, respectively. The findings from these investigations may serve as a crucial stepping stone towards the remediation of polluted water facilitated by implementing such highly efficient photocatalysts.

Sustainable and Green Synthesis of Iron Nanoparticles Supported on Natural Clays via Palm Waste Extract for Catalytic Oxidation of Crocein Orange G Mono Azoic Dye

In this study, the removal of Crocein Orange G dye (COG) from aqueous solution was investigated using an innovative green catalyst to overcome problems with chemical techniques. Clay bentonite El Hamma (HB)-supported nanoscale zero-valent iron (NZVI) was used as a heterogeneous Fenton-like catalyst for the oxidation of harmful COG. Palm waste extract was herein used as a reducing and capping agent to synthesize NZVI, and HB clay was employed, which was obtained from the El Hamma bentonite deposit in the Gabes province of Tunisia. HB and HB-NZVI were characterized by various techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer, Emmett, and Teller (BET), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), X-ray diffraction (XRD), and zeta potential. Under optimal conditions, total degradation of COG was attained within 180 min. Kinetic studies showed that the dye degradation rate followed well the pseudo-second-order model. The apparent activation energy was 33.11 kJ/mol, which is typical of a physically controlled reaction. The degradation pathways and mineralization study revealed that the adsorption-Fenton-like reaction was the principal mechanism that demonstrated 100% degradation efficiency of COG even after three successive runs. Obtained results suggest that HB-NZVI is an affective heterogeneous catalyst for the degradation of COG by H2O2 and may constitute a sustainable green catalyst for azoic dye removal from industrial wastewaters.

Ultrasonically assisted hydrothermal synthesis of tungsten(VI) oxide-TiO2 nanocomposites for enhanced photocatalytic degradation of non-narcotic drug paracetamol under natural solar light: insights into degradation pathway, mechanism, and toxicity assessment

Photocatalytic degradation of pharmaceutical residues through natural solar radiation represents a green and economical treatment process. In this work, ultrasonically assisted hydrothermal synthesis of WO3-TiO2 nanocomposite was carried out at 140-150 °C for 5 h and calcinated at 600 °C. The structural and optical properties of the synthesized material were investigated using techniques like XRD, FESEM/EDX, HRTEM, BET surface area, UV-DRS optical analysis, and photocurrent response. The band gap of TiO2 was successfully reduced from 3.0 to 2.54 eV and thus making it effective under solar light. Complete degradation of paracetamol (50 ppm and natural pH of 6.5) was achieved in 3.5 h under natural sunlight at catalyst dose of 0.5 g/l. The extent of mineralization was evaluated by measuring the COD reduction. Based on the degradation products identified by GC-MS/LC-TOF-MS, the degradation process under natural solar-light could be interpreted to initiate through OH. radical species. The toxicity removal of the treated paracetamol solution under natural solar-light was evaluated by the seed germination test using Spinacia oleracea seeds and exhibited 66.70% seed germination, confirming the reduction in toxicity. The enhanced photocatalytic efficiency of the nanocomposite is attributed to the higher surface area, low rutile content, lower band gap, and incorporation of WO3, which led to an extended absorption range and a slower rate of electron-hole recombination. The technical insights presented in this research offer a feasible approach for utilizing natural solar light driven photocatalysis for wastewater treatment in an efficient and sustainable way. The proposed degradation pathway, and seed germination test (toxicity removal) of the treated paracetamol solution under natural sunlight, has not been previously evaluated.

A Z-scheme CdS/Ag3PO4 catalyst: Characterization, experimental design and mechanism consideration for methylene blue

Due to the explosive use of Azo dyes in various industries such as textiles, discharging these industrial effluents into the environment critically polluted water supplies. Accordingly, constructing/developing novel binary catalysts to diminish the pollution extent of such effluents before discharging into environment is an excellent issue in environmental chemistry. Here, a binary CdS/ Ag₃PO₄ was constructed, and its boosted photocatalytic activity was proven against methylene blue (MB), as a model dye pollutant. The Wurtzite CdS and Ag₃PO₄ cubic crystal nanoparticles were synthesized and coupled mechanically. The binary sample's lowest photoluminescence (PL) results confirm a higher e/h separation. DRS results confirmed a decreased energy gap for the coupled system. The semiconductors' VB and CV potentials were calculated and used for constructing of Z-scheme mechanism. The photocatalytic activity was followed via an experimental design approach. The model F-value of 89.75 > F_0.05,14,13 = 2.42 and LOF F-value of 6.57 < F_{0.05,10, 3} = 8.79 reveal that the model well processed data. The optimal run conditions were CMB: 5 ppm, Catalyst dose: 1 g/L, pH: 3.25, and irradiation time: 139 min, at which 85% of MB molecules were degraded. Based on the trend of ascorbic acid > isopropanol > formic acid ≈ nitrate obtained for the scavengers' importance in decreasing the photocatalyst activity, superoxide radicals had the highest effect in MB degradation and then ^•OH. The results showed the direct Z-scheme has the main effect on MB degradation by the binary sample.

Cerium-based metal sulfide derived nanocomposite-embedded rGO as an efficient catalyst for photocatalytic application

Reduced graphene oxide (rGO) with metal sulfides is an efficient photocatalyst for treating textile effluent. Herein, a hydrothermal technique was used to synthesize transition metal sulfide with rGO nanocomposite. Under 120 min of sunlight exposure, the cerium-nickel sulfide/rGO nanocomposite (Ce₂S₃-NiS₂/rGO) photodegraded the methyl orange (MO) dye with an efficiency of 89.1% which is significantly higher than that of bare nickel sulfide (NiS₂) and cerium sulfide (Ce₂S₃) photocatalysts. Moreover, another model pollutant dye bromophenol blue (BP) was treated under the same experimental condition, and it has achieved about 84.2% degradation efficiency. The combination of NiS₂ and Ce₂S₃ improves the separation efficiency of photogenerated carriers, resulting in improved photocatalytic activity. In addition, ternary metal sulfide with rGO increases pollutant adsorption and electron-hole photogenerated pairs. Therefore, the mechanism of photocatalytic Ce₂S₃-NiS₂/rGO is investigated in detail. This research could pave the way for the development of capable and adaptable Ce₂S₃-NiS₂/rGO photocatalysts for environmental remediation.

Construction of a novel double S-scheme structure WO3/g-C3N4/BiOI: Enhanced photocatalytic performance for antibacterial activity

In recent years, the threat to human health from bacteria in wastewater has attracted attention, and photocatalytic technology has emerged as a promising strategy for inactivating bacteria in water. Therefore, it is of great research value to develop a novel high-efficiency photocatalytic system with the visible light response. We successfully designed a double S-scheme heterojunction composite WO₃/g-C₃N₄/BiOI (WCB) in this paper. The preparation of WCB composites was demonstrated by a series of characterizations, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). The antibacterial effects of photocatalysts against representative Gram-negative strain Escherichia coli (E. coli) and Gram-positive strain Staphylococcus aureus (S. aureus) were tested under LED light irradiation. The novel photocatalyst presented excellent antibacterial properties, inactivating E. coli in 12 min and S. aureus in 20 min. The bacterial cell inactivation process was studied by scanning electron microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). Active species capture experiments show that the active species present in the WCB composites in the process of inactivating bacteria are h⁺, e^-, OH and O₂^-. In conclusion, the synthesized double S-scheme WCB photocatalyst exhibits remarkable photocatalytic antibacterial activity under LED light and has broad prospects for practical application in water antibacterial treatment.

Modulation of the Structure of the Conjugated Polymer TMP and the Effect of Its Structure on the Catalytic Performance of TMP-TiO2 under Visible Light: Catalyst Preparation, Performance and Mechanism

The photocatalytic activity of titanium dioxide (TiO₂) is largely hindered by its low photoresponse and quantum efficiency. TiO₂ modified by conjugated polymers (CPs) is considered a promising approach to enhance the visible light responsiveness of TiO₂. In this work, in order to investigate the effect of CP structural changes on the photocatalytic performance of TiO₂ under visible light, trimesoyl chloride-melamine polymers (TMPs) with different structural characteristics were created by varying the parameters of the polymerisation process of tricarbonyl chloride (TMC) and melamine (M). The TMPs were subsequently composited with TiO₂ to form complex materials (TMP-TiO₂) using an in situ hydrothermal technique. The photocatalytic activity of TMP-TiO₂ was evaluated by the degradation of rhodamine B (RhB). The results showed that the trend of the structure of the TMP with the reaction conditions was consistent with the visible light responsiveness of TMP-TiO₂, and TMP (1:1)-TiO₂ had the best photocatalytic activity and could degrade 96.1% of the RhB. In conclusion, our study provided new insights into the influence of the structural changes of TMPs on the photocatalytic activity of TMP-TiO₂ under visible light, and it improves our understanding of how conjugated polymers affect the photocatalytic activity of TiO₂ under visible light.

Sulfate radicals-based advanced oxidation processes for the degradation of pharmaceuticals and personal care products: A review on relevant activation mechanisms, performance, and perspectives

Owing to the rapid development of modern industry, a greater number of organic pollutants are discharged into the water matrices. In recent decades, research efforts have focused on developing more effective technologies for the remediation of water containing pharmaceuticals and personal care products (PPCPs). Recently, sulfate radicals-based advanced oxidation processes (SR-AOPs) have been extensively used due to their high oxidizing potential, and effectiveness compared with other AOPs in PPCPs remediation. The present review provides a comprehensive assessment of the different methods such as heat, ultraviolet (UV) light, photo-generated electrons, ultrasound (US), electrochemical, carbon nanomaterials, homogeneous, and heterogeneous catalysts for activating peroxymonosulfate (PMS) and peroxydisulfate (PDS). In addition, possible activation mechanisms from the point of radical and non-radical pathways are discussed. Then, biodegradability enhancement and toxicity reduction are highlighted. Comparison with other AOPs and treatment of PPCPs by the integrated process are evaluated as well. Lastly, conclusions and future perspectives on this research topic are elaborated.

Simultaneous decolorization of anionic and cationic dyes by 3D metal-free easily separable visible light active photocatalyst

To overcome the hard and costly post-treatment separation of ultrathin graphitic carbon nitride nanosheets (UGCN), it was supported on polyurethane foam (PUF). The ratio of PUF/UGCN was optimized for the removal of a mixture of methylene blue (MB) and methyl orange (MO) dyes. The characteristics of the composite photocatalyst and its photocatalytic performance were detailly studied. The X-ray diffraction and Fourier transform infrared results proved the successful preparation of UGCN and PUF and that the PUF/UGCN composite combines the features of both pure materials. The transmission electron microscopy illustrated the ultrathin nanosheet shape of the UGCN, while the scanning electron microscope showed the highly porous 3D-hierarchical structure of PUF. Compared to the pure components, the composite photocatalyst with PUF/UGCN mass ratio of 4 achieved better decolorization of MO and almost same decolorization of MB as UGCN. Neutral pH and 1 g/L of the composite photocatalyst were the optimum conditions for MB/MO mixture decolorization. The composite photocatalyst kept its efficiency for five successive cycles. Hydroxyl radicals were the dominant in the degradation of MB, while superoxide radicals were the most influencer in MO degradation. Conclusively, supporting UGCN onto PUF kept the photocatalytic efficiency of UGCN toward MB decolorization and improved its efficiency toward MO. Moreover, it enabled the reuse of the composite photocatalyst and facilitated the post-treatment separation process.

A core/shell TiO2 magnetized molecularly imprinted photocatalyst (MMIP@TiO2): synthesis and its photodegradation activity towards sulfasalazine

Although the selectivity of TiO₂ for the degradation of target molecules is not enough, it is a broadly employed photocatalyst for the degradation of many pollutants. Molecularly imprinted compounds owing to their extreme recognition specificity have become increasingly popular for preparing selective photocatalysts. In this work, based on molecularly imprinted magnetized TiO₂ (MMIP@TiO₂), a selective photocatalyst was prepared. Via the co-precipitation method, Fe₃O₄ particles were prepared and coated respectively by SiO₂, vinyl end groups, and molecularly imprinted polymers (MIP). The synthesized photocatalyst was characterized by the X-ray diffraction method (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive x-ray spectrometry (EDX), vibrating sample magnetometry (VSM), high-performance liquid chromatography (HPLC), and photoluminescence analysis (PL). The photocatalyst was then used to degrade the sulfasalazine pharmaceutical pollutant under UV irradiation. An average crystallite size of 9 nm was obtained for the MMIP@TiO₂ sample from the Scherrer formula and 34.5 nm by the Williamson-Hall formula. The results revealed that compared to the non-imprinted counterpart, the molecularly imprinted photocatalyst had significantly higher efficiency and selectivity for the degradation of target molecules. The process was forwarded with 90% efficiency within 10 min. Optimal conditions were 10.0 min irradiation when 25 mL SSZ solution (50 mg/L), 0.07 g/L catalyst dose, and pH 6.0 were applied. The maximum removal efficiency was calculated to be 92%. The external magnetic field quickly removed the photocatalyst from the solution and regenerated it. It was revealed that after each regeneration cycle, the efficiency dropped. Nevertheless, 63% of the preliminary effectiveness remained after four regeneration steps.

The Ultrahigh Adsorption Capacity and Excellent Photocatalytic Degradation Activity of Mesoporous CuO with Novel Architecture

In this paper, mesoporous CuO with a novel architecture was synthesized through a conventional hydrothermal approach followed by a facile sintering procedure. HR-TEM analysis found that mesoporous CuO with an interconnected pore structure has exposed high-energy crystal planes of (002) and (200). Theoretical calculations indicated that the high-energy crystal planes have superior adsorption capacity for H⁺ ions, which is critical for the excellent adsorption and remarkable photocatalytic activity of the anionic dye. The adsorption capacity of CuO to methyl orange (MO) at 0.4 g/L was approximately 30% under adsorption equilibrium conditions. We propose a state-changing mechanism to analyze the synergy and mutual restraint relation among the catalyst CuO, H⁺ ions, dye and H₂O₂. According to this mechanism, the degradation rate of MO can be elevated 3.5 times only by regulating the MO ratio in three states.

Facile synthesis of broom stick like FeOCl/g-C3N5 nanocomposite as novel Z-scheme photocatalysts for rapid degradation of pollutants

A simple and cost-effective route has been utilized for the preparation of a novel lamellar structured FeOCl/g-C₃N₅ nanocomposite as Z-scheme photocatalyst. The preparation method was performed under the ambient temperature conditions without any hazardous chemicals. Various characterization techniques, namely XRD, FESEM, TEM, FT-IR, UV-Vis, DRS, and PL were carried out to analyse the nanocomposite for confirmation of FeOCl/g-C₃N₅ nanocomposite. To evaluate its and visible light degradation performances tetracycline (T-C) was used as target pollutant. Among the optimum loading for the g-C₃N₅ incorporated FeOCl binary nanocomposites, the g-C₃N₅/FeOCl exhibited a superlative degradation performance toward the T-C antibiotic pollutant. The results confirmed that 95% of T-C was degraded within 40 min under photodegradation mechanism. The improved photodegradation performance in degradation of T-C was mainly due to the reduction in electron-hole recombination, broadening in the light absorption by g-C₃N₅ incorporation, which leads to shortening the degradation time. Furthermore, the hydroxyl and superoxide radicals played a major role in the photodegradation process and the possible mechanism was elucidated and proposed. The present work implies a novel, sustainable, and efficient Z-scheme system that may deliver a convenient method for environment remediation.

Nanomaterials photocatalytic activities for waste water treatment: a review

Water is necessary for the survival of life on Earth. A wide range of pollutants has contaminated water resources in the last few decades. The presence of contaminants incredibly different dyes in waste, potable, and surface water is hazardous to environmental and human health. Different types of dyes are the principal contaminants in water that need sudden attention because of their widespread domestic and industrial use. The toxic effects of these dyes and their ability to resist traditional water treatment procedures have inspired the researcher to develop an eco-friendly method that could effectively and efficiently degrade these toxic contaminants. Here, in this review, we explored the effective and economical methods of metal-based nanomaterials photocatalytic degradation for successfully removing dyes from wastewater. This study provides a tool for protecting the environment and human health. In addition, the insights into the transformation of solar energy for photocatalytic reduction of toxic metal ions and photocatalytic degradation of dyes contaminated wastewater will open a gate for water treatment research. The mechanism of photocatalytic degradation and the parameters that affect the photocatalytic activities of various photocatalysts have also been reported.

g-C3N4-Based Direct Z-Scheme Photocatalysts for Environmental Applications

Photocatalysis represents a promising technology that might alleviate the current environmental crisis. One of the most representative photocatalysts is graphitic carbon nitride (g-C3N4) due to its stability, cost-effectiveness, facile synthesis procedure, and absorption properties in visible light. Nevertheless, pristine g-C3N4 still exhibits low photoactivity due to the rapid recombination of photo-induced electron-hole (e−-h+) pairs. To solve this drawback, Z-scheme photocatalysts based on g-C3N4 are superior alternatives since these systems present the same band configuration but follow a different charge carrier recombination mechanism. To contextualize the topic, the main drawbacks of using g-C3N4 as a photocatalyst in environmental applications are mentioned in this review. Then, the basic concepts of the Z-scheme and the synthesis and characterization of the Z-scheme based on g-C3N4 are addressed to obtain novel systems with suitable photocatalytic activity in environmental applications (pollutant abatement, H2 production, and CO2 reduction). Focusing on the applications of the Z-scheme based on g-C3N4, the most representative examples of these systems are referred to, analyzed, and commented on in the main text. To conclude this review, an outlook of the future challenges and prospects of g-C3N4-based Z-scheme photocatalysts is addressed.

The boosted activity of AgI/BiOI nanocatalyst: a RSM study towards Eriochrome Black T photodegradation

Nowadays, critical environmental pollution needs some novel, simple, effective, and cost-effective catalysts with high efficiency in the visible region of the light. Thus, the AgI/BiOI coupled nanocatalyst sample (CS) was prepared and briefly characterized. The pH_pzc values of 6.2, 5.4, and 4.5 were estimated for AgI, BiOI, and AgI/BiOI samples. Based on the PXRD results, average crystallite sizes of 35.2, 34.7, and 34.1 nm were obtained for AgI, BiOI, and AgI/BiOI samples from the Scherrer formula and 38.3, 25.6, and 25.6 nm by the Williamson-Hall formula. SEM image confirmed a sheet-like BiOI morphology covered by AgI nanoparticles. The simultaneous interactions of the influencing variables on the boosted photocatalytic activity of CS sample towards Eriochrome Black T (EBT) were evaluated by response surface methodology (RSM) (under 100-W tungsten lamp irradiation with 230 mW/m².nm irradiance). The goodness of the model was confirmed by the significance of the model (F value of 65.68 > F_{0.05, 14, 13} = 2.55) and a non-significant LOF (F value of 0.97 < F_{0.05, 10, 3} = 8.79) at a 95% confidence interval obtained in ANOVA analysis of the results. The center point runs have the following conditions: catalyst dose: 0.68 g/L; pH: 7.5; C_EBT: 7.25 mg/L; and irradiation time: 53.5 min, while the optimal run included the following conditions: catalyst dose: 1.0 g/L; pH: 4; C_EBT: 10 mg/L; and irradiation time: 80 min. About 95% of EBT molecules were degraded in the optimal conditions.

Recent progress on ultrasound-assisted electrochemical processes: A review on mechanism, reactor strategies, and applications for wastewater treatment

The electrochemical advanced oxidation processes (EAOPs) have received significant attention among the many other water and wastewater treatment technologies. However, achieving a desirable removal effect with a single technique is frequently difficult. Therefore, the integration of ultrasound technique with other processes such as electrocoagulation, electro-Fenton, and electrooxidation is a critical way to achieve effective organic pollutants decomposition from wastewater. This review paper is focused on ultrasound-assisted electrochemical (US/electrochemical) processes, so-called sonoelectrochemical processes of various organic pollutants. Emphasis was given to recently published articles for discussing the results and trends in this research area. The use of ultrasound and integration with electrochemical processes has a synergistic impact owing to the physical and chemical consequences of cavitation, resulting in enhancing the mineralization of organic pollutants. Various types of sonoelectrochemical reactors (batch and continuous) employed in the US/electrochemical processes were reviewed. In addition, the strategies to avoid passivation, enhanced generation of reactive oxygen species, and mixing effect are reviewed. Finally, concluding remarks and future perspectives on this research topic are also explored and recommended.

Preparation of In/Sn Nanoparticles (In3Sn and InSn4) by Wet Chemical One-Step Reduction and Performance Study

The preparation of binary alloys by surfactant-assisted chemical reduction in aqueous solution at room temperature has become a hot topic. In this article low melting point tin/indium (Sn/In) nanoparticles are synthesized. The formation process of the alloy was studied. Scanning electron microscopy, energy spectrometry, and X-ray diffraction are used to determine the morphology, composition, and crystal structure of the nanoparticles. Study found that fully alloyed indium-tin nanoparticles can be obtained by wet chemical method and the main phases of indium-tin alloy are β-phase (In3Sn) and γ-phase (InSn4). However, the Sn phase appears at a low content of indium (40 wt%). When the content of indium increases to 45 (wt%), the tin phase disappears. In addition, the most important finding is that the composition of the indium-tin alloy can be changed by ratio control, and the content of In3Sn increases with the increase of indium content. The relative content of In3Sn attains a maximum when the content of indium increases to 60 (wt%). In contrast, the content of InSn4 decreases. Finally, differential scanning calorimetry measurements is performed to understand the melting behavior of the nanoparticles and low melting temperatures are achieved for a wide range of indium compositions (from 40% to 60%). The melting temperature is found to be in the range of 125–132 °C and it increased with increasing In3Sn (also the increase of indium content). This gives us a new understanding into the binary alloy nano-system and gives important information for the application of low temperature alloy solders. The choice of composition can be based on the corresponding melting point.

Fabrication of CdS/Ti3C2/g-C3N4NS Z-scheme composites with enhanced visible light-driven photocatalytic activity

The Ti3C2 and g-C3N4NS were obtained first, and the CdS/Ti3C2/g-C3N4NS Z-scheme composites were prepared via a facile hydrothermal synthesis, and their photocatalytic properties were investigated. The g-C3N4NS with a high surface area displayed higher adsorption and degradation capacity. Compared with Ti3C2/g-C3N4NS and CdS, the visible light photocatalytic activity of CdS/Ti3C2/g-C3N4NS composites was improved. The as-synthesized CTN-4:1 composite exhibited outstanding photocatalytic performance for degradation of orange II, approximately 3.2 and 10.7 times higher than that of Ti3C2/g-C3N4NS and CdS, respectively. The fabrication of CdS/Ti3C2/g-C3N4NS Z-scheme heterostructure using Ti3C2 as electron transfer medium improved the separation ability of the photoinduced e--h+ pairs, thereby leading to the improvement of visible light-driven photocatalytic activity. This finding provides new insights into the construction of high efficiency Z-scheme heterostructure photocatalyst.

Microplastics in the environment and in commercially significant fishes of mud banks, an ephemeral ecosystem formed along the southwest coast of India

Microplastic pollution and the impacts they generate on the marine ecosystem and its biota is a major global concern of recent decades. The present study was conducted to evaluate the spatio-temporal distribution of microplastics in the surface waters, sediments, and their subsequent ingestion by the commercially important fishes of Alappuzha Mud banks, a transient ecosystem formed in the littoral zones of the southwest coast of India exclusively during the Indian summer monsoon. Sampling conducted over three periods, Pre-mud bank (Pre-MB), Mud bank (MB), and Post mud bank (Post-MB) extending over three depths (2 m, 5 m and 18 m), along the semi-circular patch of mudbanks revealed marked spatio-temporal variability in microplastic distribution. In both surface water and sediments, microplastic concentration was comparatively high during MB than in Pre-MB and Post-MB periods. Spatially, during MB, the microplastic concentration was high at 5 m where the dampening of waves occurred concomitant to the thick fluid mud formation. In contrast, during Post-MB, with the subsequent dissipation of MB's and less wave dampening, the microplastics aggregated at 5 m were transported to both inshore (2 m) and offshore (18 m), thus raising their concentration at these depths. Likewise, the microplastic ingestion was more in fishes caught during MB (41%) than Post-MB (30%) and Pre-MB (29%) periods indicating increased uptake corresponding to the higher incidences in their ambient environment. Microplastic ingestion was more among pelagic planktivores, S. gibbosa (38%), A. chacunda (20%) and R. kanagurta (13%) compared to the demersal fishes. White coloured fragments of size 1-5 mm of polypropylene were the dominant microplastic in the surface waters, sediment and fishes analysed. The present study indicates the critical role of wind speed, rainfall, wave patterns, and the fluid muddy environment in regulating the microplastics distribution in a transient ecosystem formed along the southwest coast of India.

MoS2/N-TiO2/Ti mesh plate for visible-light photocatalytic ozonation of naproxen and industrial wastewater: comparative studies and artificial neural network modeling

This paper presents the results of visible-light assisted photocatalytic ozonation for the degradation of naproxen as a model pharmaceutical pollutant from water using MoS₂/N-TiO₂ immobilized on a titanium mesh plate in addition to treatment of a real industrial wastewater. The batch studies were performed for naproxen degradation by varying the reaction variables such as ozone flow rate, initial pH and pollutant concertation. It was observed that almost 90% degradation was achieved at pH = 4, ozone flow rate = 3 L min^-1 and initial naproxen concentration = 5 mg L^-1. The catalyst exhibited constant activity even after seven successive cycles. Comparative studies among sorption, ozonation, photocatalysis, catalytic ozonation and photocatalytic ozonation revealed that the later process had the highest degradation of pollutant. Moreover, an artificial neural network (ANN) model was developed to simulate the performance of visible-light photocatalytic ozonation in naproxen degradation. The developed ANN model could estimate the visible-light photocatalytic ozonation process under the different experimental conditions. Finally, the applicability of the photocatalytic ozonation was successfully approved for industrial wastewater treatment. The results showed that the COD removal efficiency reached 65% within 150 min. HIGHLIGHTS: • MoS₂/N-TiO₂/Ti was synthesized by the quick electrophoretic deposition method. • The catalyst showed good ability in naproxen degradation via visible-light photocatalytic ozonation. • A three-layer artificial neural network model was developed to predict the naproxen degradation. • Naproxen degradation efficiency through the photocatalytic ozonation was higher than the individual methods. • COD of real wastewater was reduced significantly after the visible-light photocatalytic ozonation process.

Au nanoparticles decorated polypyrrole-carbon black/g-C3N4 nanocomposite as ultrafast and efficient visible light photocatalyst

Modification and bandgap engineering are proposed to be extremely significant in improving the photocatalytic activity of novel photocatalysts. The current research focused on the fabrication of ultrafast and efficient visible light-responsive ternary photocatalyst containing g-C₃N₄ nanostructures in conjugation with polypyrrole doped carbon black (PPy-C) and gold (Au) nanoparticles by highly effectual, simple, and straightforward methodology. Various analytical techniques like XRD, FESEM, TEM, XPS, FTIR, and UV-Vis spectroscopy were applied for characterization purposes. The XRD and XPS results confirmed the successful creation of a nanocomposite framework among Au, PPy-C and g-C₃N₄. The TEM images revealed that bare g-C₃N₄ holds sheets or layered graphitic structure with sizes ranging from 100 to 300 nm. The sponge-like PPy-C network intermingled perfectly with g-C₃N₄ sheets along with homogeneously distributed 5-15 nm Au nanoparticles. The band gap energy (E_g) for bare g-C₃N₄, PPy-C/g-C₃N₄ and Au@PPy-C/g-C₃N₄ nanocomposites were found to be 2.74, 2.68, and 2.60 eV, respectively. The photocatalytic activity for all newly designed photocatalysts have been assessed during the degradation of insecticide Imidacloprid and methylene blue (MB) dye, where Au@PPy-C/C₃N₄ was found to be extremely efficient with ultrafast removal of both imidacloprid and MB in just 25 min of visible light irradiation. It was revealed that the Au@PPy-C/g-C₃N₄ ternary photocatalyst removed 96.0% of target analyte imidacloprid, which is ⁓ 2.91 times more efficient than bare g-C₃N₄ in treating imidacloprid. This report provides a distinctly promising, highly effectual and straightforward route to destruct extremely toxic and notorious pollutants and opens a new gateway in the present challenging scenario of environmental concerns.