Bio-inspired hierarchical hetero-architectures of in-situ C-doped g-C3N4 grafted on C, N co-doped ZnO micro-flowers with booming solar photocatalytic activity

Enhancing photocatalytic destruction of lignin via cellulose derived carbon quantum dots/g-C3N4 heterojunctions

Lignocellulosic biomass exhibits a promising potential for production of carbon materials. Nitrogen and phosphorus co-doped carbon quantum dots (N,P-CQDs) were fabricated via (NH4)2HPO4 assisted hydrothermal treatment of cellulose pulp fibers. The as-prepared N,P-CQDs were characterized by HRTEM, FTIR, fluorescence and UV-vis, and then incorporated into g-C3N4 (CN) through sonication and liquid deposition, forming N,P-CQDs/sonication treated g-C3N4 (C-SCN) composites, which were then explored as photocatalysts. The photocatalytic ability of C-SCN towards model lignin was further analyzed. The results showed that, the fluorescence intensity and photoluminescence performance of N,P-CQDs were much higher than that of CQDs; the heterojunction was successfully constructed between the composites of N,P-CQDs and SCN; the incorporation of N,P-CQDs enhanced the visible light absorption, but reduced the band gap of the composite heterojunction; the resultant photocatalysts exhibited a good photocatalytic ability of model lignin via catalyze the fracture of β-O-4' ether bond and CC bond, i.e., the photocatalytic degradation ratio reached up to 95.5 %; and the photocatalytic reaction generated some valuable organics such as phenyl formate, benzaldehyde, and benzoic acid. This study would promote the high value-added utilization of lignocellulosic resources especially in the transformation of lignin, conforming the concept of sustainable development.

Graphitic Carbon Nitride/Zinc Oxide-Based Z-Scheme and S-Scheme Heterojunction Photocatalysts for the Photodegradation of Organic Pollutants

Graphitic carbon nitride (g-C3N4), a metal-free polymer semiconductor, has been recognized as an attractive photocatalytic material for environmental remediation because of its low band gap, high thermal and photostability, chemical inertness, non-toxicity, low cost, biocompatibility, and optical and electrical efficiency. However, g-C3N4 has been reported to suffer from many difficulties in photocatalytic applications, such as a low specific surface area, inadequate visible-light utilization, and a high charge recombination rate. To overcome these difficulties, the formation of g-C3N4 heterojunctions by coupling with metal oxides has triggered tremendous interest in recent years. In this regard, zinc oxide (ZnO) is being largely explored as a self-driven semiconductor photocatalyst to form heterojunctions with g-C3N4, as ZnO possesses unique and fascinating properties, including high quantum efficiency, high electron mobility, cost-effectiveness, environmental friendliness, and a simple synthetic procedure. The synergistic effect of its properties, such as adsorption and photogenerated charge separation, was found to enhance the photocatalytic activity of heterojunctions. Hence, this review aims to compile the strategies for fabricating g-C3N4/ZnO-based Z-scheme and S-scheme heterojunction photocatalytic systems with enhanced performance and overall stability for the photodegradation of organic pollutants. Furthermore, with reference to the reported system, the photocatalytic mechanism of g-C3N4/ZnO-based heterojunction photocatalysts and their charge-transfer pathways on the interface surface are highlighted.

The synergistic degradation of pollutants in water by photocatalysis and PMS activation

In recent years, the synergistic degradation of water pollutants through advanced oxidation technology has emerged as a prominent research area due to its integration of various advanced oxidation technologies. The combined utilization of peroxymonosulfate (PMS) activation technology and photocatalysis demonstrates mild and nontoxic characteristics, enabling the degradation of water pollutants across a wide pH range. Moreover, this approach reduces the efficiency of electron hole recombination, broadens the catalyst's light response range, facilitates electron transfer of PMS, and ultimately improves its photocatalytic performance. The paper reviews the current research status of photocatalytic technology and PMS activation technology, respectively, while highlighting the advancements achieved through the integration of photocatalytic synergetic PMS activation technology for water pollutant degradation. Furthermore, this review delves into the mechanisms involving both free radicals and nonradicals in the reaction process and presents a promising prospect for future development in water treatment technology. PRACTITIONER POINTS: Degradation of water pollutants by photocatalysis and PMS synergistic action has emerged. Synergism can enhance the generation of free radicals. This technology can provide theoretical support for actual wastewater treatment.

Facile synthesis of hollow spherical g-C3N4@LDH/NCQDs ternary nanostructure for multifunctional antibacterial and photodegradation activities

Heterojunction nanostructure construction and morphology engineering are considered to be effective approaches to improve photocatalytic performance. Herein, ternary hierarchical hollow structures consisting of cobalt-aluminum-layered double hydroxide (CoAl-LDH) nanoplates grown on hollow carbon nitride spheres (HCNS) and decorated with N-doped carbon quantum dots (NCQDs) were prepared using a templating method and a subsequent solvothermal process. The obtained HCNS@LDH/NCQD composites presented an improved performance in photocatalytic degradation of tetracycline and inactivation of E. coli compared with pure HCNS and LDH under visible light illumination. The enhanced photocatalytic activity of the designed photocatalyst could be attributed to the following reasons: (1) A special hollow structure provides more active sites and has multiple capabilities of light reflection by helping with a high specific surface area that improves the harvesting efficiency of solar light and (2) the strong synergistic effect among the constituents, which promotes separation and transfer of charge carriers and broadens the photo-response range.

Facile preparation of cellulose nanocrystals/ZnO hybrids using acidified ZnCl2 as cellulose hydrolytic media and ZnO precursor

Hybridization of nanocellulose with zinc oxide nanoparticles can improve the dispersibility of the zinc oxide and bring new functions to the bio-based products. In this study, cellulose nanocrystal/zinc oxide (CNC/ZnO) nanohybrids with reinforcing and antibacterial properties were prepared via a facile one-pot route. Microcrystalline cellulose (MCC) was first treated with acidified zinc chloride and hydrolyzed into CNCs, which then served as a stabilizing and supporting agent for the in-situ growth of ZnO nanoparticles during subsequent chemical precipitation. The acidified ZnCl₂ solution played a dual role, acting both as cellulose hydrolytic media and as ZnO precursor. By adjusting the pH of the zinc precursor solution (pH = 9-12), well-dispersed rod-like (length: 137.0-468.0 nm, width: 54.1-154.1 nm) and flower-like (average diameter: 179.6 nm) ZnO nanoparticles with hexagonal wurtzite structure were obtained. CNC/ZnO nanohybrids were incorporated into waterborne polyurethane (WPU) films. The Young's modulus and tensile strength of the nanocomposite films increased gradually from 154.8 to 509.0 MPa and from 16.5 to 29.9 MPa, respectively, with increasing CNC/ZnO nanofiller content up to 10 wt%. The 10 % CNC/ZnO composites showed inhibition rates to both E. coli and S. aureus above 88.8 %.

Rational design of ZnO-zeolite imidazole hybrid nanoparticles with reduced charge recombination for enhanced photocatalysis

Semiconducting zinc oxide nanoparticles (ZnO NPs) hold great potential as photocatalysts in wastewater treatment because of their favorable bandgap and cost-effectiveness. Unfortunately, ZnO NPs usually show rapid charge recombination that limits their photocatalytic efficacy significantly. Herein, we report a facile way of modifying ZnO NPs with zeolite imidazole framework-8 (ZIF8). A synergy between the two components may tackle the drawback of fast charge recombination for pristine ZnO NPs. Improved performance of photocatalytic degradation of methylene blue (MB) is confirmed by comparing with pristine ZnO and ZIF8 as the catalysts. The ZIF8 in the composite serves as a trap for photogenerated electrons, thus reducing the rate of charge recombination to enhance the photocatalysis rate. In addition, the hybridization process suppresses the aggregation of ZnO NPs, providing a large surface area and a greater number of active sites. Moreover, a small shift in the absorption band of ZnO@ZIF8 (10) NPs towards higher wavelength, also witnessed a little contribution towards enhanced photocatalytic properties. Mechanistic studies of the photocatalytic process of MB using ZnO@ZIF8 NPs catalyst reveal that hydroxyl radicals are the major reactive oxygen species. The facile hybridization of ZnO with ZIF8 provides a strategy for developing new photocatalysts with wide application potential.

Processing of natural fibre and method improvement for removal of endocrine-disrupting compounds

Persistent endocrine-disrupting compounds (EDCs) in bodies of water are a concern for human health and constitute an environmental issue, even if present in trace amounts. Conventional treatment systems do not entirely remove EDCs from discharge effluent. Due to the ultra-trace level of EDCs which affect human health and pose an environmental issue, developing new approaches and techniques to remove these micropollutants from the discharged effluent is vital. This review discusses the most common methods of eliminating EDCs through preliminary, primary, secondary and tertiary treatments. The adsorption process is favoured for EDC removal, as it is an economical and straightforward option. The NABC aspects, which are the need, approach, benefits and challenges, were analysed based on existing circumstances, highlighting biochar as a green and renewable adsorbent for the removal of organic contaminants. From the environmental point of view, the effectiveness of this method, which uses natural fibre from the kenaf plant as a porous and economical biochar material with a selected lignocellulosic biomass, provides insights into the advantages of biochar-derived adsorbents. Essentially, the improvement of the natural fibre as an adsorbent is a focus, using carbonisation, activation, and the physiochemical process to enhance the adsorption ability of the material for pollutants in bodies of water. This output will complement sustainable water management approaches presented in previous studies for combating the emerging pollutant crisis via novel green and environmentally safe options.

Copper(II)-β-cyclodextrin immobilized on graphitic carbon nitride nanosheets as a highly effective catalyst for tandem oxidative amidation of benzylic alcohols

In this study, an efficient catalyst based on graphitic carbon nitride nanosheets (CN) and copper(II) supported β-cyclodextrin (β-CD/Cu(II)) was synthesized and used for tandem oxidative amidation of benzylic alcohols. In this regard, CN was functionalized by β-CD/Cu(II) via 1,3-dibromopropane linker (CN-Pr-β-CD/Cu(II)). The prepared catalyst was characterized using FT-IR, XRD, FE-SEM, EDS, TGA, ICP-OES, BET, and TEM analyses. CN-Pr-β-CD/Cu(II) was subsequently applied in a direct oxidative amidation reaction and it was observed that different benzyl alcohols were converted to desire amides with good to excellent efficiency. This reaction was performed in the presence of amine hydrochloride salts, tert-butyl hydroperoxide (TBHP), and Ca₂CO₃ in acetonitrile (CH₃CN) under nitrogen atmosphere. CN-Pr-β-CD/Cu(II) can be recycled and reused five times without significant reduction in reaction efficiency.

Insight into the activity of TiO2@nitrogen-doped hollow carbon spheres supported on g-C3N4 for robust photocatalytic performance

Designing an advance nanostructure semiconductor is an efficient strategy to promote the charge separation and thus improve the photocatalytic activity. Herein, a relatively high recombination rate of electron-hole pairs and low specific surface area of g-C₃N₄ (GCN) were subjected to the surface deposition of the core shell nanoparticles composed of nitrogen doped hollow carbon spheres (N-HCSs) as the supporting scaffold and TiO₂ nanoparticles as the photoactive layer. The ternary composites with different TiO₂@N-HCS content were prepared through a simplified nanocasting method followed by the two consecutive hydrothermal process. The effects of nitrogen doping in carbon framework, and nanoparticles amount were evaluated on the photocatalytic ability through the photodegradation of tetracycline (TC) molecules under the visible light irradiation. At the optimum content of core shell nanoparticles (7 wt%), the solar-driven TC photocatalytic degradation for ternary composite was approximately 85%, which was much better (about three times) than that of the pure GCN. More interestingly, the experimental results revealed that doping of nitrogen atoms has a positive role on the charge separation and the resulting photocatalytic efficiency. The employed hollow carbon spheres here play three important roles: (1) providing a substrate to uniformly dispersion of TiO₂ nanoparticles without any aggregation; (2) reducing the combination of charge carriers and improving the separation of photoinduced carriers; (3) formation of larger surface area and more active sites on the photocatalyst surface. Furthermore, the underlying photocatalytic degradation mechanism was introduced by the controlled experiments using photoluminescent and radical scavenger tests.

A Comprehensive Review of Graphitic Carbon Nitride (g-C3N4)-Metal Oxide-Based Nanocomposites: Potential for Photocatalysis and Sensing

g-C3N4 has drawn lots of attention due to its photocatalytic activity, low-cost and facile synthesis, and interesting layered structure. However, to improve some of the properties of g-C3N4, such as photochemical stability, electrical band structure, and to decrease charge recombination rate, and towards effective light-harvesting, g-C3N4-metal oxide-based heterojunctions have been introduced. In this review, we initially discussed the preparation, modification, and physical properties of the g-C3N4 and then, we discussed the combination of g-C3N4 with various metal oxides such as TiO2, ZnO, FeO, Fe2O3, Fe3O4, WO3, SnO, SnO2, etc. We summarized some of their characteristic properties of these heterojunctions, their optical features, photocatalytic performance, and electrical band edge positions. This review covers recent advances, including applications in water splitting, CO2 reduction, and photodegradation of organic pollutants, sensors, bacterial disinfection, and supercapacitors. We show that metal oxides can improve the efficiency of the bare g-C3N4 to make the composites suitable for a wide range of applications. Finally, this review provides some perspectives, limitations, and challenges in investigation of g-C3N4-metal-oxide-based heterojunctions.

Hierarchically Porous ZnO/g-C3N4 S-Scheme Heterojunction Photocatalyst for Efficient H2O2 Production

The design of photocatalysts with hierarchical pore sizes is an effective method to improve mass transport, enhance light absorption, and increase specific surface area. Moreover, the construction of a heterojunction at the interface of two semiconductor photocatalysts with suitable band positions plays a crucial role in separating and transporting charge carriers. Herein, ZIF-8 and urea are used as precursors to prepare hierarchically porous ZnO/g-C₃N₄ S-scheme heterojunction photocatalysts through a two-step calcination method. This S-scheme heterojunction photocatalyst shows high activity toward photocatalytic H₂O₂ production, which is 3.4 and 5.0 times higher than that of pure g-C₃N₄ and ZnO, respectively. The mechanism of charge transfer and separation within the S-scheme heterojunction is studied by Kelvin probe, in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS), and electron paramagnetic resonance (EPR). This research provides an idea of designing S-scheme heterojunction photocatalysts with hierarchical pores in efficient photocatalytic hydrogen peroxide production.

Highly efficient visible light active Cu-ZnO/S-g-C3N4 nanocomposites for efficient photocatalytic degradation of organic pollutants

The photocatalytic activity of photocatalysts is severely hampered by limited visible light harvesting and unwanted fast recombination of photogenerated e^- and h⁺. In the current study, the photocatalytic efficiency of Cu-ZnO/S-g-C₃N₄ (CZS) nanocomposites was investigated against MB dye. The composite materials were designed via chemical co-precipitation method and characterised by important analytical techniques. Distinctive heterojunctions developed between S-g-C₃N₄ and Cu-ZnO in the CZS composite were revealed by TEM. The synthesized composites exhibit a huge number of active sites, a large surface area, a smaller size and better visible light absorption. The considerable enhancement in the photocatalytic activity of CZS nanocomposites might be accredited to the decay in the e-h pair recombination rate and a red shift in the visible region, as observed by PL and optical analysis, respectively. Furthermore, the metal (Cu) doping into the S-g-C₃N₄/ZnO matrix created exemplary interfaces between ZnO and S-g-C₃N₄, and maximized the photocatalytic activity of CZS nanocomposites. In particular, CZS nanocomposites synthesized by integrating 25% S-g-C₃N₄ with 4% Cu-ZnO (CZS-25 NCs) exhibited the 100% photocatalytic degradation of MB in 60 minutes under sunlight irradiation. After six cycles, the photocatalytic stability of CZS-25 NCs was excellent. Likewise, a plausible MB degradation mechanism is proposed over CZS-25 NCs based on photoluminescence and reactive species scavenger test observation. The current research supports the design of novel composites for the photocatalytic disintegration of organic contaminants.

BiFeO3 immobilized within liquid natural rubber-based hydrogel with enhanced adsorption-photocatalytic performance

Semiconductor materials have shown a good photocatalytic behaviour for the photodegradation of organic pollutants. In this work, maleated liquid natural rubber (MLNR) based hydrogel supported bismuth ferrite (BiFeO₃) as photocatalyst was successfully synthesized by crosslinking with acrylic acid (AAc) assisted by the ultrasonication method to study the efficiency for the removal of methylene blue (MB) dye in wastewater. Response surface methodology (RSM) was used to optimize the parameters for adsorption of the methylene blue (MB) dye compound, whereby the effects of the initial concentration of MB and the adsorption time were examined to obtain a quadratic model for the respective hydrogel composite. The prepared composite sample was characterized by Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) and X-ray Diffraction (XRD) analysis. Remarkable improvement for removal of methylene blue (99% removal) was found within 3 h adsorption time with a MLNR/AAc-BiFeO₃ hydrogel composite as compared to the pristine hydrogel. A synergistic mode of dye removal by adsorption and photodegradation is proposed. Based on the isotherm and kinetic study conducted, it was found that Freundlich isotherm model and a pseudo second-order kinetic model was best fitted for adsorption of MB dye. The MLNR/AAc-BiFeO₃ composite maintains its removal efficiency after 5 cycles without the necessity of post-treatment separation. Therefore, it is crucial to note that the resultant low-cost MLNR/AAc-BiFeO₃ hydrogel composite in this study offers excellent potential for water and wastewater treatment applications with improved recyclability and recovery.

Cellulose controlled zinc oxide nanoparticles with adjustable morphology and their photocatalytic performances

The cellulose fibers with different size and aspect ratio was used as the matrix for the controllable preparation of zinc oxide (ZnO) to synthesize ZnO/cellulose composite catalyst with adjustable photocatalytic properties. The ZnO with different morphology of sphere, sheet, and flower, was in-situ synthesized on cellulose fibers by chemical deposition method, the flower-like ZnO supported on cellulose fiber exhibited the best photocatalytic activity. Furthermore, with the decrease of fiber size, the morphology of ZnO changed from most sheet to fully self-assembled flower shape, and the average thickness of nanosheets was increased. Cellulose fibers with smaller size and higher aspect ratio were more likely to form a 3D network structure with rich pores and stable mechanical properties. Significantly, with the decreasing of fiber size, ZnO/NFC has excellent photocatalytic efficiency (100 %). All ZnO/cellulose composites can be recycled more than five times.

Recent advances in photodegradation of antibiotic residues in water

Antibiotics are widely present in the environment due to their extensive and long-term use in modern medicine. The presence and dispersal of these compounds in the environment lead to the dissemination of antibiotic residues, thereby seriously threatening human and ecosystem health. Thus, the effective management of antibiotic residues in water and the practical applications of the management methods are long-term matters of contention among academics. Particularly, photocatalysis has attracted extensive interest as it enables the treatment of antibiotic residues in an eco-friendly manner. Considerable progress has been achieved in the implementation of photocatalytic treatment of antibiotic residues in the past few years. Therefore, this review provides a comprehensive overview of the recent developments on this important topic. This review primarily focuses on the application of photocatalysis as a promising solution for the efficient decomposition of antibiotic residues in water. Particular emphasis was laid on improvement and modification strategies, such as augmented light harvesting, improved charge separation, and strengthened interface interaction, all of which enable the design of powerful photocatalysts to enhance the photocatalytic removal of antibiotics.

Starch bio-template synthesis of W-doped CeO2 catalyst for selective catalytic reduction of NOx with NH3: influence of ignition temperature

A novel tungsten-doped CeO₂ catalyst was fabricated via the sweet potato starch bio-template spread self-combustion (SSC) method to secure a high NH₃-SCR activity. The study focuses on the influence of ignition temperature on the physical structure and redox properties of the synthesized catalyst and the catalytic performance of NO_x reduction with NH₃. These were quantitatively examined by conducting TG-DSC measurements of the starch gel, XRD analysis for the crystallites, SEM and TEM assessments for the morphology of the catalyst, XPS and H₂-TPR measurements for the distribution of cerium and tungsten, and NH₃-TPD assessments for the acidity of the catalyst. It is found that the ignition temperature shows an important role in the interaction of cerium and tungsten species, and the optimal ignition temperature is 500 °C. The increase of ignition temperature from 150 °C is beneficial to the interactions of species in the catalyst, depresses the formation of WO₃, and refines the cubic CeO₂ crystallite. The sample ignited at 500 °C shows the biggest BET surface area, the highest surface concentration of Ce species and molar ratio of Ce³⁺/(Ce³⁺+Ce⁴⁺), and the most abundant surface Brønsted acid sites, which are the possible reasons for the superiority of the NH₃-SCR activity. With a high GHSV of 200,000 mL (g h)^-1 and the optimal ignition temperature, Ce₄W₂O_z-500 can achieve a steadily high NO_x reduction of 80% or more at a lowered reduction temperature in the range of 250~500 °C.

Photodecomposition of ibuprofen over g-C3N4/Bi2WO6/rGO heterostructured composites under visible/solar light

A microwave-assisted hydrothermal preparation of heterostructured graphitic carbon nitride/bismuth tungsten oxide/reduced graphene oxide nanocomposites (denoted as GBR-T, T = microwave irradiation time) is performed. The prepared GBR-T photocatalysts are identified by employing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), time-resolved photoluminescence (TRPL) and nitrogen adsorption-desorption isotherms. The photocatalytic performance of these GBR-T is evaluated by the photocatalytic degradation of ibuprofen (IBP) under the visible light (λ > 420 nm) and solar light irradiation. Among all prepared photocatalysts, ca. 93% of IBP photodegradation can be achieved with a degradation rate constant (k) of 0.011 min^-1 under visible-light irradiation upon the optimal microwave-assisted reaction time of 60 min. The improvement is primarily attributable to the higher crystallization degree, specific surface area and increased charge transfer efficiency as verified by XRD, nitrogen adsorption-desorption isotherms and TRPL, respectively. The photocatalytic performance of this catalyst is further enhanced in the photodecomposition of IBP (ca. 98.6%) under sun light irradiation. The electron spin resonance (ESR) and liquid chromatography-mass/mass spectrometry (LC-MS/MS) studies show that the superoxide radicals and hydroxyl radicals are the dominant active species in the photocomposition of IBP and degradation intermediates are formed through three probable photodegradation pathways. This investigation provides a simple way to prepare triple 2D heterojuction photocatalysts which could be effectively used in the advanced oxidation process for removal of emerging contaminants in wastewater by using renewable energy.

Preparation and Photocatalytic Performance of Dumbbell Ag2CO3-ZnO Heterojunctions

Dumbbell Ag₂CO₃-ZnO heterojunctions were synthesized for the first time via a simple in situ precipitation method. The as-prepared Ag₂CO₃-ZnO heterojunction showed high photocatalytic activity in the decomposition of methyl orange aqueous solution under simulated solar irradiation. The high improvement of photocatalytic activity compared to that of pure ZnO can be attributed to the formation of the Ag₂CO₃-ZnO heterojunction. Furthermore, the mechanism of photocatalytic activity was investigated in detail. The free radical trapping experiments indicated that the superoxide radical (·O₂ ^-) was an important active species in the photocatalytic process. This paper provides a new prospect for the preparation of photocatalysts with high catalytic performance in the degradation of dye wastewater.