Fabrication of novel magnetically separable nanocomposites using graphitic carbon nitride, silver phosphate and silver chloride and their applications in photocatalytic removal of different pollutants using visible-light irradiation

Elucidating the catalytic mechanism of Prussian blue nanozymes with self-increasing catalytic activity

Although Prussian blue nanozymes (PBNZ) are widely applied in various fields, their catalytic mechanisms remain elusive. Here, we investigate the long-term catalytic performance of PBNZ as peroxidase (POD) and catalase (CAT) mimetics to elucidate their lifespan and underlying mechanisms. Unlike our previously reported Fe3O4 nanozymes, which exhibit depletable POD-like activity, the POD and CAT-like activities of PBNZ not only persist but slightly enhance over prolonged catalysis. We demonstrate that the irreversible oxidation of PBNZ significantly promotes catalysis, leading to self-increasing catalytic activities. The catalytic process of the pre-oxidized PBNZ can be initiated through either the conduction band pathway or the valence band pathway. In summary, we reveal that PBNZ follows a dual-path electron transfer mechanism during the POD and CAT-like catalysis, offering the advantage of a long service life.

An Eco-Friendly Synthesis Approach for Enhanced Photocatalytic and Antibacterial Properties of Copper Oxide Nanoparticles Using Coelastrella terrestris Algal Extract

Background

In the current scenario, the synthesis of nanoparticles (NPs) using environmentally benign methods has gained significant attention due to their facile processes, cost-effectiveness, and eco-friendly nature.

Methods

In the present study, copper oxide nanoparticles (CuO NPs) were synthesized using aqueous extract of Coelastrella terrestris algae as a reducing, stabilizing, and capping agent. The synthesized CuO NPs were characterized by X-ray diffraction (XRD), UV-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and field emission scanning electron microscopy (FE-SEM) coupled with energy-dispersive X-ray spectroscopy (EDS).

Results

XRD investigation revealed that the biosynthesized CuO NPs were nanocrystalline with high-phase purity and size in the range of 4.26 nm to 28.51 nm. FTIR spectra confirmed the existence of secondary metabolites on the surface of the synthesized CuO NPs, with characteristic Cu-O vibrations being identified around 600 cm-1, 496 cm-1, and 440 cm-1. The FE-SEM images predicted that the enhancement of the algal extract amount converted the flattened rice-like structures of CuO NPs into flower petal-like structures. Furthermore, the degradation ability of biosynthesized CuO NPs was investigated against Amido black 10B (AB10B) dye. The results displayed that the optimal degradation efficacy of AB10B dye was 94.19%, obtained at 6 pH, 50 ppm concentration of dye, and 0.05 g dosage of CuO NPs in 90 min with a pseudo-first-order rate constant of 0.0296 min-1. The CuO-1 NPs synthesized through algae exhibited notable antibacterial efficacy against S. aureus with a zone of inhibition (ZOI) of 22 mm and against P. aeruginosa with a ZOI of 17 mm.

Conclusion

Based on the findings of this study, it can be concluded that utilizing Coelastrella terrestris algae for the synthesis of CuO NPs presents a promising solution for addressing environmental contamination.

Progress of charge carrier dynamics and regulation strategies in 2D CxNy-based heterojunctions

Two-dimensional carbon nitrides (CxNy) have gained significant attention in various fields including hydrogen energy development, environmental remediation, optoelectronic devices, and energy storage owing to their extensive surface area, abundant raw materials, high chemical stability, and distinctive physical and chemical characteristics. One effective approach to address the challenges of limited visible light utilization and elevated carrier recombination rates is to establish heterojunctions for CxNy-based single materials (e.g. C2N3, g-C3N4, C3N4, C4N3, C2N, and C3N). The carrier generation, migration, and recombination of heterojunctions with different band alignments have been analyzed starting from the application of CxNy with metal oxides, transition metal sulfides (selenides), conductive carbon, and Cx'Ny' heterojunctions. Additionally, we have explored diverse strategies to enhance heterojunction performance from the perspective of carrier dynamics. In conclusion, we present some overarching observations and insights into the challenges and opportunities associated with the development of advanced CxNy-based heterojunctions.

Strategic rationalization for improved photocatalytic decomposition of toxic pollutants: Immobilizing Bi2Te3 nanorods and V2O5 nanoparticles over MoS2 nanosheets

Researchers have become increasingly interested in solar energy based on semiconductor photocatalysts to remove hazardous pollutants and clean the environment. In this work, an efficient MoS2-Bi2Te3-V2O5 nanocomposite has been prepared through wet impregnation method. MoS2-Bi2Te3-V2O5 photocatalyst was utilized to decompose the MB and Rh B dyes. The photocatalytic efficiency (Rh B) of MoS2-Bi2Te3-V2O5 nanocomposite (95.19 %) was higher than 2.70 times of Bi2Te3 nanorods, 1.55 times of V2O5 nanoparticles, 1.68 times of MoS2 nanosheets, 1.50 times of MoS2-Bi2Te3, and 1.21 times of MoS2-V2O5 nanocomposite, respectively. Recycling tests conducted on the MoS2-Bi2Te3-V2O5 nanocomposite revealed its high stability and durability. The outcomes obtained from the scavenger test suggest that the photogenerated hydroxyl radicals play a chief role in the photocatalytic performance of Rh B dye in the MoS2-Bi2Te3-V2O5 nanocomposite, respectively. The enhanced photocatalytic performance of the MoS2-Bi2Te3-V2O5 nanocomposite is ascribed to the strong hybrid formation of Bi2Te3, V2O5, and MoS2 nanosheets, respectively. Consequently, the straightforward and readily synthesized MoS2-Bi2Te3-V2O5 nanocomposite can serve as an economical, highly effective material for environmental applications.

A highly sensitive TiO2-based molecularly imprinted photoelectrochemical sensor with regulation of imprinted sites by Photo-deposition

Molecularly imprinted photoelectrochemical sensors (MIPES) have gained significant attention in the detection field due to their high selectivity and accuracy. However, their sensitivity still needs improvement. Here we developed a TiO2-based MIPES (TiO2 NRs/NiOOH/rMIP) to detect ciprofloxacin (CIP). We identified the photoactive sites of TiO2 by NiOOH photo-deposition and anchored the imprinted sites on the photoactive sites by complexation between CIP and NiOOH. By regulating the imprinted sites, the photocurrent difference before and after the addition of CIP increases and the detection sensitivity of CIP is improved. Moreover, a PN heterojunction is formed between TiO2 and NiOOH, which enables rapid transfer of photoexcited holes and electrons to different semiconductors under the built-in electric field. This leads to improved photoactivity of TiO2 and further increases the sensitivity of MIPES. Compared with sensors prepared by the traditional electro-polymerization CIP and Molecularly imprinted polymers (TiO2 NRs/NiOOH/eMIP), TiO2 NRs/NiOOH/rMIP as constructed in this work displays higher sensitivity, wider linear detection range, and lower limit of detection (LOD). Additionally, TiO2 NRs/NiOOH/rMIP shows good selectivity, stability, and recovery rate, and has a promising application prospect in the actual detection of antibiotics.

Fe3O4/CuO/Chitosan Nanocomposites: An Ultrasound-Assisted Green Approach for Antibacterial and Photocatalytic Properties

The fundamental goal of this research was to use an environmentally friendly sonochemical method to synthesize a Fe3O4/CuO/chitosan magnetic nanocomposite. The nanocomposites featured particle sizes ranging from 50 to 90 nm, and structural characteristics were thoroughly examined. Moreover, the material displayed selective photodegradation capabilities with MB, achieving an impressive efficiency of nearly 98% within 180 min under specific conditions. Notably, the material's reusability was remarkable, maintaining an efficiency of approximately 88% even after five cycles. The possible photodegradation mechanism was proposed based on the evaluation of energy bands, along with a comprehensive analysis of the impacts on MB photodegradation. Concurrently, adsorption isotherms and kinetic models were evaluated. Additionally, this material exhibited promising antibacterial activity against Saccharomyces cerevisiae, Bacillus subtilis, and Escherichia coli. These findings suggested that the Fe3O4/CuO/chitosan material could be utilized in real-world scenarios for environmental purification due to its ability to function as a photocatalyst and antibacterial agent.

Recent advances in g-C3N4-based photocatalysis for water treatment: Magnetic and floating photocatalysts, and applications of machine-learning techniques

Over the past decade, there has been a substantial increase in research investigating the potential of graphitic carbon nitride (g-C3N4) for various environmental remediations. Renowned for its photocatalytic activity under visible light, g-C3N4 offers a promising solution for treating water pollutants. However, traditional g-C3N4-based photocatalysts have inherent drawbacks, creating a disparity between laboratory efficacy and real-world applications. A primary practical challenge is their fine-powdered form, which hinders separation and recycling processes. A promising approach to address these challenges involves integrating magnetic or floating materials into conventional photocatalysts, a strategy gaining traction within the g-C3N4-based photocatalyst arena. Another emerging solution to enhance practical applications entails merging experimental results with contemporary computational methods. This synergy seeks to optimize the synthesis of more efficient photocatalysts and pinpoint optimal conditions for pollutant removal. While numerous review articles discuss the laboratory-based photocatalytic applications of g-C3N4-based materials, there is a conspicuous absence of comprehensive coverage regarding state-of-the-art research on improved g-C3N4-based photocatalysts for practical applications. This review fills this void, spotlighting three pivotal domains: magnetic g-C3N4 photocatalysts, floating g-C3N4 photocatalysts, and the application of machine learning to g-C3N4 photocatalysis. Accompanied by a thorough analysis, this review also provides perspectives on future directions to enhance the efficacy of g-C3N4-based photocatalysts in water purification.

Asterarcys quadricellulare algae-mediated copper oxide nanoparticles as a robust and recyclable catalyst for the degradation of noxious dyes from wastewater

The present article explores the synthesis of copper oxide nanoparticles (CuO NPs) utilizing Asterarcys quadricellulare algal extract and examines the effect of various reaction parameters on the size and morphology of the nanoparticles. The samples were thoroughly characterized using XRD, FTIR, UV-vis, FE-SEM, and EDS techniques. The XRD analysis disclosed that the size of the synthesized nanoparticles could be controlled by adjusting the reaction parameters, ranging from 4.76 nm to 13.70 nm along the highest intensity plane (111). FTIR spectroscopy provided evidence that the phytochemicals are present in the algal extract. We have compared the photocatalytic activity of biologically and chemically synthesized CuO NPs and observed that biologically synthesized CuO NPs showed better photocatalytic activity than chemically synthesized CuO NPs. The biosynthesized CuO NPs (S8) demonstrated outstanding photodegradation activity towards four different organic dyes, namely BBY, BG, EBT, and MG, with degradation percentages of 95.78%, 98.02%, 94.15%, and 96.04%, respectively. The maximum degradation efficacy of 98.02% was observed for the BG dye at optimized reaction conditions and 60 min of visible light exposure. The kinetics of the photodegradation reaction followed the pseudo-first-order kinetic model, and the rate constant (k) was calculated using the Langmuir-Hinshelwood model for each dye. This study provides an efficient and sustainable approach for synthesizing CuO NPs with superior photocatalytic degradation efficiency towards organic dyes.

Degradation of cefadroxil drug by newly designed solar light responsive alcoholic template-based lanthanum ferrite nanoparticles

In this work, lanthanum ferrite nanoparticles were synthesized via a simple co-precipitation method. Two different templates, namely sorbitol and mannitol, were used in this synthesis to tune the optical, structural, morphological, and photocatalytic properties of lanthanum ferrite. The synthesized lanthanum ferrite-sorbitol (LFOCo-So) and lanthanum ferrite-mannitol (LFOCo-Mo) were investigated through Ultraviolet-Visible (UV-Vis), X-ray diffraction (XRD), Fourier Transform Infra-Red (FTIR), Raman, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX), and photoluminescence (PL) techniques to study the effects of the templates on the tunable properties of lanthanum ferrite nanoparticles. The UV-Vis study revealed a remarkably small bandgap (2.09 eV) of LFOCo-So compared to the LFOCo-Mo having a band gap of 2.46 eV. XRD analysis revealed a single-phased structure of LFOCo-So, whereas LFOCo-Mo showed different phases. The calculated crystallite sizes of LFOCo-So and LFOCo-Mo were 22 nm and 39 nm, respectively. FTIR spectroscopy indicated the characteristics of metal-oxygen vibrations of perovskites in both lanthanum ferrite (LFO) nanoparticles, whereas a slight shifting of Raman scattering modes in LFOCo-Mo in contrast to LFOCo-So showed the octahedral distortion of the perovskite by changing the template. SEM micrographs indicated porous particles of lanthanum ferrite with LFOCo-So being more uniformly distributed, and EDX confirmed the stoichiometric ratios of the lanthanum, iron, and oxygen in the fabricated lanthanum ferrite. The high-intensity green emission in the photoluminescence spectrum of LFOCo-So indicated more prominent oxygen vacancies than LFOCo-Mo. The photocatalytic efficiency of synthesized LFOCo-So and LFOCo-Mo was investigated against cefadroxil drug under solar light irradiation. At optimized photocatalytic conditions, LFOCo-So showed higher degradation efficiency of 87% in only 20 min than LFOCo-Mo having photocatalytic activity of 81%. The excellent recyclability of the LFOCo-So reflected that it could be reused without affecting photocatalytic efficiency. These findings showed that sorbitol is a useful template for the lanthanum ferrite particles imparting outstanding features, enabling it to be used as an efficient photocatalyst for environmental remediation.

Determining the Photoelectrical Behavior and Photocatalytic Activity of an h-YMnO3 New Type of Obelisk-like Perovskite in the Degradation of Malachite Green Dye

YMnO₃ is a P-type semiconductor with a perovskite-type structure (ABO₃). It presents two crystalline systems: rhombohedral and hexagonal, the latter being the most stable and studied. In the hexagonal system, Mn³⁺ ions are coordinated by five oxygen ions forming a trigonal bipyramid, and the Y³⁺ ions are coordinated by five oxygen ions. This arrangement favors its ferroelectric and ferromagnetic properties, which have been widely studied since 1963. However, applications based on their optical properties have yet to be explored. This work evaluates the photoelectric response and the photocatalytic activity of yttrium manganite in visible spectrum wavelengths. To conduct this, a rod-obelisk-shaped yttrium manganite with a reduced indirect bandgap value of 1.43 eV in its hexagonal phase was synthesized through the precipitation method. The synthesized yttrium manganite was elucidated by solid-state techniques, such as DRX, XPS, and UV-vis. It was non-toxic as shown by the 100% leukocyte viability of mice BALB/c.

Facile synthesis of NiAl2O4/g-C3N4 composite for efficient photocatalytic degradation of tetracycline

Designing high-efficiency photocatalysts responsive to visible light is important for the degradation of antibiotics in water. Heterojunction engineering is undoubtedly an effective strategy to improve the photocatalytic performance. In this work, spinel-type metal oxides (NiAl₂O₄, NAO) are synthesized by a simple sol-gel and calcination process. After compounding graphitic carbon nitride (g-C₃N₄), NAO/g-C₃N₄ heterojunction is obtained, which then is used as the photocatalyst for tetracycline hydrochloride (TC). The effects of photocatalyst dosage, the initial concentration of TC, and solution pH on photodegradation performance are systematically studied. The removal rate of TC on NAO/g-C₃N₄ reach up to ∼90% after visible light irradiation for 2 hr and the degradation rate constant is ∼7 times, and ∼32 times higher than that of pure NAO and g-C₃N₄. The significantly improved photocatalytic activity can be attributed to the synergistic effect between well matched energy levels in NAO/g-C₃N₄ heterojunctions, improvement of interfacial charge transfer, and enhancement of visible light absorption. This study provides a way for the synthesis of efficient photocatalysts and an economic strategy for removing antibiotics contamination in water.

Dual-sensitized heterojunction PDA/ZnO@MoS2 QDs combined with multilocus domino-like DNA cascade reaction for ultrasensitive photoelectrochemical biosensor

In this work, by integrating with a highly efficient multilocus domino-like cascade reaction on DNA nanonet, an ultrasensitive PEC biosensor based on dual-sensitized PDA/ZnO@MoS₂ QDs photoactive material as signal probe was proposed for detection of miRNA-182-5p. The dual-sensitized PDA/ZnO@MoS₂ QD composed by both of p-n and S-scheme heterojunctions on electrode generated an extremely high initial PEC signal, which however quenched by CdTe QDs decorated on DNA nanonet owing to the significant p-n quenching effect. Thereafter, the output DNA (RS) from DSN enzyme-assisted target recycling amplification triggered an ingenious multilocus domino-like DNA cascade reaction on DNA nanonet for releasing numerous CdTe QDs. Thanks to the multilocus domino-like mode that owned abundant binding sites for increasing trigger efficiency and drove cascade reaction automatically advance along four stated pathways, the target conversion rate could be improved effectively compared with that of traditional approaches, significantly enhancing the detection sensitivity. Consequently, the developed PEC biosensor exhibited a low detection limit to 0.17 fM, providing a new avenue for sensitive, fast and reliable sensing of various DNA/RNA.

Heterostructure charge transfer dynamics on self-assembled ZnO on electronically different single-walled carbon nanotubes

The charge transfer kinetics of the catalyst particles play a key role in advanced oxidation processes (AOP) for the complete destruction of recalcitrant and persistent contaminants in water. Here, a significant improvement in the photocatalytic performance is observed in the Single-Walled Carbon Nanotube (SWCNT)-ZnO heterostructure photocatalyst. The charge transfer dynamics and factors affecting AOP are studied using ZnO nanoparticles self-assembled onto three electronically different SWCNTs (metallic, semiconducting, and pristine) via the precipitation method, introducing a heterojunction interface. The creation of the SWCNT/ZnO heterostructure interface improves charge transfer and separation, resulting in a charge carrier lifetime of 7.37 ns. Also, surface area, pore size, and pore volumes are increased by 4.2 times compared to those of ZnO. The nanoparticles-coated face-mask fabric used as the floating photocatalyst exhibited high stability and recyclability with 99% RhB degradation efficiency under natural sunlight and 94% under UV light after the 5th cycle. The surface and crystal defects-oxygen or zinc defects/interstitials open new reaction active sites that assist in charge carrier transfer and act as pollutant absorption and interaction sites for enhanced performance. The ideal band edge positions of the valence band and conduction band favor the generation of H2O/OH•, OH·/OH, and O2/HO2• reactive oxygen species. OH• radicals are found to play a vital role in this AOP by using ethanol as an OH• scavenger.

Prediction of band edge potentials and reaction products in photocatalytic copper and iron sulfides

The prediction of band edge potentials in photocatalytic materials is an important but challenging task. In contrast, bandgaps can be easily determined through absorption spectra. Here, we present two simple theoretical approaches for the determination of band edge potentials which are based on the electron negativity and work function of each constituent atom. We use these approaches to determine band edge potentials in semiconducting metallic oxides and sulfides, such as titanium dioxide (TiO₂), chalcopyrite (CuFeS₂), pyrite (FeS₂), covellite (CuS), and chalcocite (Cu₂S) with respect to an absolute scale (eV) and an electrochemical scale (V). Until now, there is little information on iron and copper sulfides referring to these thermodynamic parameters. TiO₂ (Titania p25) was used as reference semiconductor to validate the calculation procedures using experimental values by X-ray diffraction analysis (XRD), diffuse reflectance spectrometry (DRS), and electron paramagnetic resonance spectroscopy (EPR). The production of key chemical species such as reactive oxygen species (ROS) and reactive sulfur species (RSS) has been theoretically and experimentally determined by EPR.

Synthesis and visible-light photocatalytic property of spinel CuAl2O4 for vehicle emissions

Photodegradation of vehicle emissions is a promising approach for dealing with atmospheric pollution in road tunnels. In this research, copper aluminate nanoparticles (CuAl₂O₄) were prepared by the sol-gel method using copper nitrate, aluminum nitrate, and citric acid as precursor materials. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis spectroscopy to validate their structure, surface morphology, and optical properties, respectively. The XRD and SEM results confirm that the CuAl₂O₄ powder has a particle size of 20-37 nm and exhibits a spinel-type structure. The upper limit of the stimulation wavelength in the UV-Vis diffuse reflectance spectrum is located at 725 nm with a band gap (Eg) of about 1.50 eV, which is suitable for effective visible-light degradation. Photocatalytic performance of the CuAl₂O₄ nanoparticles was analyzed by investigating the effects of light source, calcination temperature, and catalyst loading amount on the degradation of vehicle emissions (CO, HC, and NO). Best results were obtained under fluorescent light irradiation by CuAl₂O₄ nanoparticles calcined at 700 °C. The optimum catalyst amount for decomposing CO, HC, and NO were determined as 0.5 g, 0.5 g, and 2 g, respectively. Overall, the photocatalytic performance study verifies that spinel CuAl₂O₄ photocatalyst is a valuable material for next-generation technologies aimed at reducing harmful emissions from vehicles.

Direct Z-Scheme CoFe2O4-Loaded g-C3N4 Photocatalyst with High Degradation Efficiency of Methylene Blue under Visible-Light Irradiation

Magnetically recyclable direct Z-scheme CoFe2O4-loaded g-C3N4 photocatalyst material was fabricated using a facile hydrothermal technique and subsequently characterized by XRD, VSM, PL, FT-IR, EDX, DRS, SEM, and BET techniques. The characterization results confirmed that nanoparticles of CoFe2O4 are loaded on the surface of g-C3N4 sheets. The optical band gap of g-C3N4 has been decreased from 2.65 eV to 1.30 eV by means of the loading of CoFe2O4 nanoparticles onto the nanosheets of g-C3N4. This has enhanced the separation process of electron-hole. Under visible light irradiation, the photocatalytic activity of the developed direct Z-scheme CoFe2O4-loaded g-C3N4 photocatalyst was evaluated for the photodegradation of methylene blue (MB); during this process the MB decomposed by up to 98.86% in 140 min. Meanwhile, under the same irradiation and time conditions, the g-C3N4 and CoFe2O4 themselves degraded MB up to 74.92% and 51.53%, respectively. The direct Z-scheme CoFe2O4-loaded g-C3N4 material was recovered from the solution after the photocatalytic activity using an external magnet and studied to determine its stability. It was shown that the photoactivity did not change significantly after five consecutive cycles.

Efficient photo-Fenton catalysis using magnetic iron nanoparticles decorated boron nitride quantum dots: theoretical and experimental investigations

To achieve the efficient removal of pharmaceutical wastes, novel photo-Fenton catalysts, iron-decorated boron nitride quantum dots (Fe@BNQDs) were prepared. Fe@BNQDs were characterized using XRD, SEM-EDX, FTIR, and UV-Vis spectrophotometry. The decoration of Fe on the surface of BNQDs enhanced the catalytic efficiency due to the photo-Fenton process. Photo-Fenton catalytic degradation of folic acid was investigated under UV and visible light. The influence of H₂O₂, catalyst dose, and temperature on the degradation yield of folic acid was investigated using Response Surface Methodology. Moreover, the efficiency of the photocatalysts and kinetics was investigated. Radical trapping experiments revealed that holes were the main dominant species in the photo-Fenton degradation mechanism and BNQDs played active roles because of their hole extraction ability. Additionally, active species such as e^- and O₂ ^-˙ have a medium effect. The computational simulation was utilized to provide insights into this fundamental process, and for this purpose, electronic and optical properties were calculated.

Visible active narrow/narrow band gap CuO/Cu2SnS3 nanoheterostructures as efficient nanophotocatalysts

Binary metal oxide/ternary metal sulphide based nanoheterostructures, such as CuO/Cu₂SnS₃, were prepared via a modified hydrothermal route. The prepared nanoheterostructures were characterized using scanning electron microscopy, x-ray powder diffractometer, XPS, ultraviolet-visible spectroscopy, isoelectric point, and Brunauer-Emmett-Teller techniques. The XPS results revealed the successful incorporation of Cu⁺/Cu²⁺ with different ratios. The prepared heterostructures were tested as solar active photocatalysts for Methylene Blue (MB) photodegradation. The CuO/Cu₂SnS₃ (20% Cu₂SnS₃/80% CuO) photocatalytic results exhibited a high photodegradation efficiency (90%) after 60 min. In addition, the photonic efficiency values (ζ) were calculated to be 15.9%, 44%, and 61.4% for CuO, Cu₂SnS₃, and CuO/Cu₂SnS₃ nanoheterostructures, respectively. In addition, the reactive oxidative species were detected by the trapping experiments to get a clear insight about the photocatalytic reactivity factors. Total organic carbon (TOC) was conducted to confirm the safe photodegradation of MB dye without the formation of colorless hazardous (95.5% TOC removal). Based on the electronic band structure, the mechanism of photodegradation was investigated. The currently investigated heterostructure system is narrow/narrow bandgap, which fulfills the two contradictory conditions in terms of high solar photocatalytic activity and overcomes the rapid recombination process.

Construction of Z-scheme Ti/Ga co-doped ZnO heterostructure photocatalyst with graphitic carbon nitride for efficient visible-light-driven dye degradation

Innovative solar-driven heterostructure photocatalysts are promising for removing the organic contaminants in the water environment. In this work, a sequence of well-defined Z-scheme Ti-Ga co-doped ZnO/g-C₃N₄ (TGZ/CN) heterostructure photocatalysts were developed via a simple sol-gel method and the single-phase dispersion method in order to realize the cooperative improvement from the Ti/Ga co-doping and construction of heterostructure. The synthesized samples were analyzed by a variety of characterization techniques, and the photocatalytic activity was assessed by photodegradation of methylene blue (MB) under visible light irradiation. Compared to the ZnO and g-C₃N₄, the TGZ/CN composite demonstrated higher photocatalytic performance for the degradation of MB indicating an efficient photocatalytic degradation rate of 95.4% in 105 min under visible light. Moreover, the TGZ/CN photocatalyst exhibited excellent stability after five cycles of MB photodegradation. Furthermore, the as-prepared composites' possible photocatalytic mechanism was discussed in detail. The improved photocatalytic performance primarily resulted from the effectively reduced band gap of ZnO after Ti/Ga co-doping and the facilitated separation of photoexcited e^-/h⁺ pairs caused by the construction of Z-scheme heterojunction. This work offers novel insights in developing hybrids with highly efficient photocatalytic activity towards future environmental applications.

Architecture of visible-light induced Z-scheme MoS2/g-C3N4/ZnO ternary photocatalysts for malachite green dye degradation

The synthesis of bilayer heterojunctions has received considerable attention recently. Fabrication of novel bilayer composites is of significant interest to improve their photocatalytic efficiency. In this study, molybdenum disulfide (MoS₂), a layered dichalcogenide material exhibiting unique properties, in combination with graphitic carbon nitride (g-C₃N₄), a carbon-based layered material, was fabricated with small amounts of zinc oxide (ZnO). Three composites, MoS₂/g-C₃N₄, MoS₂/ZnO, and MoS₂/g-C₃N₄/ZnO were prepared via a simple exfoliation method and characterized by various physicochemical methods. The Z-scheme charge transfer mechanism in the prepared ternary composite improves efficiency by inhibiting the recombination rate of electron-hole pairs. It has shown excellent performance in degrading a major water contaminant, malachite green (MG) dye, under visible light irradiation.

Solar-light-driven ternary MgO/TiO2/g-C3N4 heterojunction photocatalyst with surface defects for dinitrobenzene pollutant reduction

Defect engineering and heterojunction are promising strategies to improve the photocatalytic performance of particular catalyst through effective charge carrier separation and transport. Herein, we developed Z-scheme MgO/TiO₂/g-C₃N₄ ternary heterojunction photocatalyst with surface defects and effective charge separation for reduction of recalcitrant dinitrobenzene isomers under simulated solar light irradiation. Mott-Schottky (MS) plot analysis and electron spin resonance (ESR) radical trapping experiment suggested the formation of Z-scheme heterojunction at the interface of TiO₂/g-C₃N₄, which played a crucial role in the electron-hole separation. Incorporating MgO into the structure further enhances charge separation via Ti³⁺ and oxygen vacancy (OV) defects formation at the TiO₂/MgO interface as confirmed by electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analyses. Besides, the surface basicity of MgO enhanced conversion of dinitrobenzene (DNB) isomers through formation of nitrophenylhydroxylamine intermediate which can easily be reduced to phenylenediamines (PDAs). As confirmed by high performance liquid chromatography (HPLC) analysis, excellent selectivity for PDAs (95-98%) was achieved in 90 min with ternary MgO/TiO₂/g-C₃N₄ composite compared to the binary MgO/TiO₂ and TiO₂/g-C₃N₄. A possible reaction pathway and photocatalytic reduction mechanism were proposed and elucidated. This work demonstrated an effective strategy to reduce recalcitrant dinitrobenzene isomers using efficient, low-cost, and environmental benign photocatalyst with a facile identification of reaction intermediates.

Silver-Loaded Carbon and Phosphorous Co-Doped Boron Nitride Quantum Dots (Ag@CP-BNQDs) for Efficient Organic Waste Removal: Theoretical and Experimental Investigations

In this paper, silver-loaded phosphorous and carbon co-doped boron nitride quantum dot (Ag@CP-BNQD) nanocomposites were synthesized using a co-precipitation method followed by a hydrothermal approach. The nanocomposites of Ag@CP-BNQDs were characterized by scanning electron microscopy, energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and ultraviolet-visible spectrophotometry. The as-prepared Ag@CP-BNQDs were used for photocatalytic degradation of 10 common organic pollutants, including dyes, pharmaceuticals, and pesticides in aqueous solution under visible light irradiation. The high-performance photocatalysis of Ag@CP-BNQDs proved that Ag@CP-BNQDs is plasmonic and the n-p junction photocatalyst. Theoretical calculations were done to measure the crystals and electronic structures of Ag@CP-BNQDs. Theoretical results showed that loading of Ag behaves as plasmonic sensitizers and co-catalysts and provides extra bands, which make electron movement easier between valance and conduction bands. The mechanism of the charge separation enhancement was postulated. Our findings might deepen our understanding of how sensitizer surface modification works in photodegradation applications.

CdTiO3-NPs incorporated TiO2 nanostructure photocatalyst for scavenger-free water splitting under visible radiation

Nanofibrous morphology and the doping technique can overcome the problem of electron/hole fast recombination and improve the activity of titanium oxide-based photocatalysts. In this study, nanoparticulate and nanofibrous forms of CdTiO3-incorporated TiO2 were synthesized with different cadmium contents; the morphology and composition were determined by SEM, TEM, EDX, and XRD techniques. The nanomorphology, cadmium content, and reaction temperature of Cd-doped TiO2 nanostructures were found to be strongly affect the hydrogen production rate. Nanofibrous morphology improves the rate of hydrogen evolution by around 10 folds over the rate for nanoparticles due to electron confinement in 0D nanostructures. The average rates of hydrogen production for samples of 0.5 wt.% Cd are 0.7 and 16.5 ml/gcat.min for nanoparticles and nanofibers, respectively. On the other hand, cadmium doping resulted in increasing the hydrogen production rate from 9.6 to 19.7 ml/gcat.min for pristine and Cd-doped (2 wt%) TiO2 nanofibers, respectively. May be the formation of type I heterostructures between the TiO2 matrix and CdTiO3 nanoparticles is the main reason for the observed enhancement of photocatalytic activity due to the strong suppressing of electron/holes recombination process. Consequently, the proposed photocatalyst could be exploited to produce hydrogen from scavenger-free solution. Varying reaction temperature suggests that hydrogen evolution over the proposed catalyst is incompatible with the Arrhenius equation. In particular, reaction temperature was found to have a negative influence on photocatalytic activity. This work shows the prospects for using CdTiO3 as a co-catalyst in photon-induced water splitting and indicates a substantial enhancement in the rate of hydrogen production upon using the proposed photocatalyst in nanofibrous morphology.

SmMnO3-decorated ZnO in a hexane-water interface for enhancing visible light-driven photocatalytic degradation of malachite green

Malachite green (MG) contributes to water contamination because its accumulation adversely impacts aquatic systems. For the first time, we prepare a high photoresponse of ZnO/SmMnO₃ heterojunction via a high-speed stirring method at the nonpolar-polar interface assisted by Alstonia scholaris leaves extract (ASLE) as natural hydrolyzing and stabilizing agents. The heterojunction formation boosts the photocatalytic activity of ZnO up to 91.74% under visible light irradiation. Photoluminescence analysis confirmed that modification with SmMnO₃ increases the separation of photogenerated charges and plummets the recombination rates of electron-holes, which induces high photodegradation of MG. With 3 mg of catalyst, the %TOC removal efficiency for MG degradation over ZnO/SmMnO₃ was found to be 53.09%, which is higher than that over ZnO. The kinetics model for the photocatalytic reaction was a pseudo-first-order with excellent stability in four consecutive cycles with no structural change. The radical trapping experiment suggests that h⁺ was the major species in the MG photodegradation reaction. Additionally, morphology and elemental analyses clearly present the formation of ZnO/SmMnO₃ heterojunction without any impurities. The current research demonstrates a simple and advanced technique to design heterojunction photocatalyst at the interface of hexane-water.

Tunable band structure of synthesized carbon dots modified graphitic carbon nitride/bismuth oxychlorobromide heterojunction for photocatalytic degradation of tetracycline in water

In this study, graphitic carbon nitride (CN) decorated with carbon quantum dot (CQD) and bismuth oxychlorobromide (BiOCl_xBr_1-x) was fabricated by calcination and hydrothermal methods. The morphology characterization of the synthesized photocatalyst revealed that CQD and BiOCl_xBr_1-x solid solution were deposited on the CN surface. CQD served as the electron reservoir, which could reduce the recombination of electron-hole pairs, thus improving the overall photocatalytic performance. The synergistic effect of 1 wt% CQDs and BiOCl_0.75Br_0.25 markedly improved the interfacial charge transfer efficiency and light-harvesting capacity of the composite. The degradation rate of tetracycline (TC) over CN/CQD/BiOCl_0.75Br_0.25 was 83.4 % after 30 min and favorable stability with near-initial capacity under visible light irradiation. Meanwhile, the reaction mechanism of the photocatalytic performance was demonstrated by the analysis of the surface adsorption sites, efficient utilization of visible light, and charge carrier transfer. The degradation by-products and potential degradation pathways were also analyzed using liquid chromatography-mass spectrometry. Finally, the toxicity estimation software tool (T.E.S.T) analysis indicated that the toxicity of most intermediates was lower than TC. This work provideed a strategy for fabricating visible light (VL) photocatalyst with excellent photocatalytic activity, furnishing a new insight for interface charge transfer.

Preparation of Ag3PO4/CoWO4 S-scheme heterojunction and study on sonocatalytic degradation of tetracycline

In this study, 0.6Ag₃PO₄/CoWO₄ composites were synthesized by hydrothermal method. The prepared materials were systematically characterized by techniques of scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), N₂ adsorption/desorption, and UV-vis diffuse reflectance spectrum (DRS). Furthermore, the sonocatalytic degradation performance of 0.6Ag₃PO₄/CoWO₄ composites towards tetracycline (TC) was investigated under ultrasonic radiation. The results showed that, combined with potassium persulfate (K₂S₂O₈), the 0.6Ag₃PO₄/CoWO₄ composites achieved a high sonocatalytic degradation efficiency of 97.89 % within 10 min, which was much better than bare Ag₃PO₄ or CoWO₄. By measuring the electrochemical properties, it was proposed that the degradation mechanism of 0.6Ag₃PO₄/CoWO₄ is the formation of S-scheme heterojunction, which increases the separation efficiency of electron-hole pairs (e^--h⁺) and generates more electrons and holes, thereby enhancing the degradation activity. The scavenger experiments confirmed that hole (h⁺) was the primary active substance in degrading TC, and free radicals (OH) and superoxide anion radical (O₂^-) were auxiliary active substances. The results indicated that 0.6Ag₃PO₄/CoWO₄ nanocomposites could be used as an efficient and reliable sonocatalyst for wastewater treatment.

ZnCo2O4/g-C3N4/Cu nanocomposite as a new efficient and recyclable heterogeneous photocatalyst with enhanced photocatalytic activity towards the metronidazole degradation under the solar light irradiation

In this study, ZnCo₂O₄/g-C₃N₄/Cu is synthesized as a new and highly effectual solar light-driven heterogeneous photocatalyst. The prepared photocatalyst is characterized using FT-IR, XRD, XPS, DRS, FESEM, TEM, EDS, and elemental mapping techniques. The performance of ZnCo₂O₄/g-C₃N₄/Cu is studied towards the metronidazole (MNZ) degradation under solar light irradiation. The kinetics of MNZ degradation and efficacy of the operational parameters comprising the initial MNZ amount (10-30 mg L^-1), photocatalyst dosage (0.005-0.05 g L^-1), pH (3-11), and contact time (5-30 min) on the MNZ degradation process are investigated. Surprisingly, the ZnCo₂O₄/g-C₃N₄/Cu nanocomposite presents a privileged photocatalytic performance towards the MNZ degradation under solar light irradiation. The enhanced photocatalytic activity of this photocatalyst can be ascribed to the synergistic optical effects of ZnCo₂O₄, g-C₃N₄, and Cu. The value of band gap energy for ZnCo₂O₄/g-C₃N₄/Cu is estimated to be 2.3 eV based on the Tauc plot of (αhν)² vs. hν. The radical quenching experiments confirm that the superoxide radicals and holes are the principal active species in the photocatalytic degradation of MNZ, whereas the hydroxyl radicals have no major role in such degradation. The as-prepared photocatalyst is simply isolated and recycled for at least eight runs without noticeable loss of the efficiency. Using the natural sunlight source, applying a very low amount of the photocatalyst, neutrality of the reaction medium, short reaction time, high efficiency of the degradation procedure, utilizing air as the oxidant, low operational costs, and easy to recover and reuse of the photocatalyst are the significant highlights of the present method. It is supposed that the current investigation can be a step forward in the representation of an efficacious photocatalytic system in the treatment of a wide range of contaminated aquatic environments.

GaN/MgI2 van der Waals heterostructure: a two-factor tunable photocatalyst for hydrogen evolution

With the increasing environmental pollution and energy crisis, it is significant to develop environmentally friendly and adjustable photocatalysts for water splitting. Here we explored the optoelectronic properties of several H-GaN/MgI₂ vdW heterostructures by regulating different polarization surfaces and numbers of GaN layers. Our results demonstrate that all structures, except 2L-Ga-GaN/MgI₂, exhibit excellent physical stability. Moreover, the band structures and band edge positions demonstrate that only the heterostructure of 3L-Ga-GaN/MgI₂ with both suitable band alignment (type-II) and an acceptable band gap (∼1.92 eV) is most satisfactory for water splitting. Additionally, the absorption coefficient of the 3L-Ga-GaN/MgI₂ heterostructure can reach over ∼10⁵ cm^-1, which has further confirmed its excellent advantage in photocatalysis. Finally, in the case of 6% external strain for the 3L-Ga-GaN/MgI₂ heterostructure, a rollover in band alignment (from type-II to type-I) is exhibited. These promising features of the GaN/MgI₂ vdW heterostructure give a new paradigm for developing novel efficient and adjustable photocatalytic water-splitting materials.

Unraveling the MnMoO4 polymorphism: a comprehensive DFT investigation of α, β, and ω phases

The MnMoO₄ is an environmentally friendly semiconductor material widely employed in technological devices. This material can be obtained on three different polymorphs, and although such phases were reported decades ago, some obscurity over their structure and properties is still perceived. Thus, this work provides a comprehensive DFT investigation of the α, β, and ω phases of MnMoO_4, analyzing their crystalline structure, stability, and electronic and magnetic properties. The results show that all phases of MnMoO₄ are stable at room conditions connected by pressure application or long-time high-temperature treatment. The MnMoO₄ phases are G-type antiferromagnetic with semiconductor bandgap and have enormous potential to develop magnetic, optical, and electronic devices and photocatalytic-based processes. The results also evidence potential antiviral and antibacterial activities of the three MnMoO₄ polymorphs.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10853-022-07277-7.

gCN-P: a coupled g-C3N4/persulfate system for photocatalytic degradation of organic pollutants under simulated sunlight

A coupled g-C3N4/PDS system, named gCN-P, has been put forward to degrade refractory organic pollutants under simulated sunlight which integrates photocatalysis and PS-AOPs (advanced oxidation of persulfate based on sulfate radicals). The coupled g-C3N4 and PDS showed superior synergistic effect for MO degradation under simulated sunlight. Results showed that almost all MO was removed in the gCN-P system after irradiation for 80 min under simulated sunlight. The degradation rate of gCN-P system was improved by 12.6 and 4.9 times compared to single PDS and g-C3N4 systems, respectively. And only by adding 0.01 g of persulfate into the gCN-P system. The results of quenching experiments and EPR showed that O2-, 1O2 and h+ were main active species for the degradation of MO in the gCN-P system under simulated sunlight. Application of the gCN-P system in tap water samples demonstrated its excellent performance in real-world water environment, and the gCN-P system was employed for removing other new contaminants such as bisphenol A, ciprofloxacin, and paracetamol. The results demonstrated the gCN-P system can effectively remove organic pollutants under sunlight in practices.

Photocatalytic efficiency under visible light of a novel Cu-Fe oxide composite films prepared by one-step sparking process

Copper-iron (Cu-Fe) oxide composite films were successfully deposited on quartz substrate by a facile sparking process. The nanoparticles were deposited on the substrate after sparking off the Fe and Cu tips with different ratios and were then annealed at different temperatures. The network particles were observed after annealing the film at 700 °C. Meanwhile, XRD, XPS and SAED patterns of the annealed films at 700 °C consisted of a mixed phase of CuO, γ-Fe₂O₃, CuFe₂O₄ and CuFe₂O. The film with the lowest energy band gap (E_g) of 2.56 eV was observed after annealing at 700 °C. Interestingly, the optimum ratio and annealing temperature show the photocatalytic activity under visible light higher than 20% and 30% compare with the annealed TiO₂ at 500 and 700 °C, respectively. This is a novel photocatalyst which can be replaced TiO₂ for photocatalytic applications in the future.

Strategies to Enhance ZnO Photocatalyst's Performance for Water Treatment: A Comprehensive Review

Despite the photocatalytic organic pollutant degradation using ZnO started in 1910-1911, many challenges are still ahead, and several critical issues have to be addressed. Large band gap, and short life-time of photogenerated electrons and holes are critical issues negatively affect the photocatalytic activity of ZnO. Various approaches have been introduced to overcome these issues including intrinsic doping, extrinsic doping, and heterostructure. This review introduces unique and deep insights into tuning of the photocatalytic activity of ZnO. It starts by description of how to tune the photocatalytic activity of pristine ZnO through tuning its morphology, surface area, exposed face, and intrinsic defects. Afterward, the review explains how the Z-scheme approach succeed to address the redox weakened issue of heterojunction approach. In general, this review provides a clear image that helps the researcher to tune the photocatalytic activity of pristine ZnO and its heterostructure.

Chabazite Synthesis and Its Exchange with Ti, Zn, Cu, Ag and Au for Efficient Photocatalytic Degradation of Methylene Blue Dye

A chabazite-type zeolite was prepared by the hydrothermal method. Before ion exchange, the chabazite was activated with ammonium chloride (NH₄Cl). The ion exchange process was carried out at a controlled temperature and constant stirring to obtain ion-exchanged chabazites of Ti⁴⁺ chabazite (TiCHA), Zn²⁺ chabazite (ZnCHA), Cu²⁺ chabazite (CuCHA), Ag⁺ chabazite (AgCHA) and Au³⁺ chabazite (AuCHA). Modified chabazite samples were characterized by X-ray diffraction (XRD), scanning electron microscope equipped with energy-dispersive spectroscopy (SEM-EDS), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), N₂ adsorption methods and UV–visible diffuse reflectance spectroscopy (DRS). XRD results revealed that the chabazite structure did not undergo any modification during the exchange treatments. The photocatalytic activity of chabazite samples was evaluated by the degradation of methylene blue (MB) in the presence of H₂O₂ under ultraviolet (UV) light illumination. The photodegradation results showed a higher degradation efficiency of modified chabazites, compared to the synthesized chabazite. CuCHA showed an efficiency of 98.92% in MB degradation, with a constant of k = 0.0266 min⁻¹ following a first-order kinetic mechanism. Then, it was demonstrated that the modified chabazites could be used for the photodegradation of dyes.

N,P-codoped carbon quantum dots-decorated TiO2 nanowires as nanosized heterojunction photocatalyst with improved photocatalytic performance for methyl blue degradation

N,P-doped carbon quantum dots (N,P-CQDs) are deemed as a promising candidate to environmentally friendly materials owing to the inexpensive, biocompatible nature. TiO₂ nanowire is a prospective photocatalyst because of its efficient migration of photoexcited carriers in wastewater treatment. However, the N,P-CQDs-decorated TiO₂ nanowire (N,P-CQDs/NW-TiO₂) photocatalysts have been rarely reported. In this study, we build N,P-CQDs on the surface of TiO₂ nanowires via a simple deposition process. Our investigations demonstrate that N,P-CQDs/NW-TiO₂ has a great photocatalytic degradation for methyl blue (MB) under irradiation. The degradation rate of can reach 93.6% within 120 min under proper conditions. The excellent degradation performance of N,P-CQDs/NW-TiO₂ is ascribed to the mesoporous structure and high separation rate of photoexcited carriers. In addition, the N,P-CQDs/NW-TiO₂ have outstanding recycled photocatalytic capability. After being recycled four times, the N,P-CQDs/NW-TiO₂ still maintain 59.9% photocatalytic activity. The fabricated nanosized photocatalyst can be widely utilized in the field of photocatalysis for wastewater treatment.

Direct Z-scheme MgIn2S4/TiO2heterojunction for enhanced photocathodic protection of metals under visible light

To improve the photocathodic protection performance of traditional TiO₂photoanodes for metals, constructing a Z-scheme heterojunction is one of the most promising and creative strategies. Herein, we fabricated a novel Z-scheme MgIn₂S₄nanosheets/TiO₂nanotube nanocomposite through anodization and hydrothermal method. The optimized Z-scheme MgIn₂S₄/TiO₂nanocomposites exhibited stronger visible light absorption, higher separation efficiency of photoelectrons and photocathodic protection performances in comparison to pure TiO₂. The theoretical analysis and experimental results show that the Z-scheme heterojunction and oxygen vacancies jointly improved the separation efficiency of photogenerated electron-hole pairs and visible light absorption capacity, thereby improving the photoelectric conversion performance of the MgIn₂S₄/TiO₂nanocomposites. Furthermore, the influence of the precursor solution concentration on the photocathodic protection performances of the composites was investigated. As a result, when the concentration of magnesium source in the precursor solution was 0.06 mmol, the prepared MgIn₂S₄/TiO₂-0.06 displayed the best photocathodic protection performance. In addition, the hydroxyl radicals (·OH) generated in the electron spin resonance (ESR) experiment verified the Z-scheme heterojunction mechanism of the MgIn₂S₄/TiO₂composite, and also demonstrated the excellent redox performance of the composite. This work provides valuable reference for the construction of high-performance Z-scheme heterojunctions for photocathode protection of metals.

In situ composite of Co-MOF on a Ti-based material for visible light multiphase catalysis: synthesis and the photocatalytic degradation mechanism

A Co-MOF/Ti-based Z-type heterojunction prepared by an in situ growth method exhibits good photocatalytic activity for tetracycline.