Photocatalytic Water Purification Research Articles

Cooperative Design of the Ag3PO4/NH2-MIL-88B (Fe/Co) Heterojunction Integrated with Conductive Polypyrrole for Advanced Photocatalytic Water Purification.

Wastewater treatments using photocatalysts and metal-organic frameworks (MOFs) have gained increasing importance due to their catalytic reactions leading to the decomposition of dyes and organic pollutants without generating secondary pollutants. This work aims at developing an advanced photocatalytic fabric by conceiving a heterojunction of NH2-MIL-88B (Fe/Co) (n-type) and Ag3PO4 (p-type) and increasing the electrical conductivity to facilitate charge transfer at the heterojunction. Of particular interest is the design of a conductive Z-scheme heterophotocatalytic fabric by implementing polypyrrole (PPy) between the heterocatalysts and to investigate the role of the heterojunction and increased conductivity in the generation of reactive species and the photocatalytic mechanism. The electrochemical characterization evinces that the enhanced photocatalytic reaction by the conductive heterojunction is attributed to the efficient electron-hole separation and the increased redox power by the Z-scheme construction. Notably, the implementation of PPy not only accelerated the photocatalytic reactivity by the promoted charge mobility but also improved the structural stability of the catalysts by gluing them on the fabric substrate. The developed photocatalytic system demonstrated significantly enhanced purification performance compared with a single photocatalytic system and showed consistent performance with repeated use cycles. The result of this study implicates that electrical conductivity in a photocatalytic system plays a crucial role in the photocatalytic mechanism, charge mobility, and photocatalytic reactivity.

Review of Concentrated Solar Power Technology Applications in Photocatalytic Water Purification and Energy Conversion: Overview, Challenges and Future Directions

Photocatalysis, a promising semiconductor-based technology activated by free and eternal solar energy, has great potential for addressing environmental remediation and energy conversion challenges. Concentrated solar power (CSP) technologies, namely parabolic trough reflectors, solar power towers, parabolic dish reflectors and linear Fresnel reflectors, exhibited excellent feasibility for boosting solar-driven photocatalytic processes. Based on the structural characteristics of CSP technologies, the CSP-based photocatalytic reactors could be divided into concentrated types and non/low-concentrated types. This academic review comprehensively investigated the integration of CSP technology in photocatalysis, emphasizing the feasibility of sunlight as an ideal energy source. Additionally, considering the optimal light irradiance and reaction temperature demands for achieving efficient photocatalytic processes, the significance of introducing CSP into solar light-driven photocatalytic reactions was highlighted. Moreover, the current challenges that exist in CSP-based photoreactors were identified, and potential solutions were proposed accordingly. This work hopes to provide some references for the future study of CSP-based photocatalytic reactors under the theme of sustainable development.

Carbon nitride with water soluble ability: Enhanced oxygen species interphase mass transfer for homogenous photocatalytic water purification

Heterogeneous catalysis has been considered a promising way for waste purification, however the catalytic performances of the heterogeneous-based systems are still unsatisfactory, mainly due to the limited active sites exposure and sluggish reactants mass transfer. In this study, we propose a conceptual carbonitride-based quasi-homogeneous catalytic system, exhibiting remarkable photocatalytic activity toward organic pollutants degradation and pathogenic bacteria inactivation. We verify that downsizing carbonitride into nanodot level and modifying the material with hydrophilic groups can endow it with water soluble ability, forming a quasi-homogeneous catalytic system to maximize the active sites exposure and minimize the reactants mass transfer resistance for high-efficient water purification. As a result, the as-established quasi-homogeneous photocatalytic system exhibits abundant surface-active sites and reactants mass transfer efficiencies that allows remarkable O2 reduction for ROS generation. In addition, the treated water containing the functionalized carbonitride is found capable of driving the fast flocculate of suspended substance, which helps to build a well water decontamination and suspended substance removal water purification nexus for practical applications. The work demonstrated here sheds new light in designing high-efficient homogeneous catalytic system for energy and environmental related applications.

Defect-mediated time-efficient photocatalytic degradation of methylene blue and ciprofloxacin using tungsten-incorporated ternary perovskite BaSnO3 nanoparticles

Photocatalytic water purification has been extensively explored for its economic, eco-friendly, and sustainable aspects. In this study, tungsten (W) incorporated BaSn1-xWxO3 (x = 0 to 0.05) nanoparticles synthesized by facile hydrogen peroxide precipitation route has been demonstrated for photocatalytic degradation of methylene blue (MB) dye and ciprofloxacin (CIP) antibiotic. The structural analysis indicates the presence of hybrid composite-like nanostructures with reduced crystallinity. Optical studies reveal blueshift in bandgap and decrease in oxygen vacancy defects upon W-incorporation. Pure BaSnO3 shows overall enhanced photocatalytic activity towards MB (90.22%) and CIP (78.12%) after 240 min of white LED light and sunlight irradiation respectively. The 2 % W-incorporated BaSnO3 shows superior photocatalytic degradation of MB (26.89%) and CIP (45.14%) within first 30 min of irradiation confirming the presence of W to be beneficial in the process. The free radical study revealed the dominant role of reactive hole (h+) and oxygen radical (O2•−) species during photodegradation and their intermediates are investigated to elucidate the degradation mechanism of MB within 30 min of irradiation. This study is promising towards developing defect mediated and time-efficient photocatalysts for environmental remediation.

Facile microwave synthesis of Zinc Ferrite@NCDs for photocatalytic degradation of fluoroquinolone antibiotics

Zinc ferrite (ZnFe2O4) composites have attracted growing interest in photocatalytic water purification. Herein, the hybrids of zinc ferrite and nitrogen-doped carbon dots (ZnF@x%NCDs) were synthesized via facile microwave synthesis. X-ray diffraction and Raman characterization confirm the formation of the spinel structure, and elemental composition has been analyzed by X-ray photoelectron spectroscopy. The photocatalytic activity of ZnF@x%NCDs was evaluated via the decomposition of ciprofloxacin and norfloxacin under visible light illumination. We noted that 20 % weight loading of NCDs led to the highest (∼79.2 %) ciprofloxacin (CIP) degradation. Diffuse reflectance measurements demonstrate the reduction of the band gap in composites ZnF@20%NCDs (1.91 eV) compared with bare ZnF (2.03 eV); moreover, the hybridization of zinc ferrites with NCDs results in enhanced photocurrent density and surface area. The effect of experimental parameters, including the role of photocatalyst dosage, pH value, and initial concentration of pollutants on the degradation of CIP, have also been investigated.

A novel hierarchical 0D/3D NH2-MIL-101(Fe)/ZnIn2S4 S-scheme heterojunction photocatalyst for efficient Cr(VI) reduction and photo-Fenton-like removal of 2-nitrophenol

In this work, we designed a new hierarchical 0D/3D NH2-MIL-101(Fe)/ZnIn2S4 (NM-101(Fe)/ZIS) S-scheme heterojunction photocatalyst using a simple oil bath technique, in which nanometer-sized NM-101(Fe) are extensively scattered on the surface of ZIS microspheres. In contrast to an acidic environment, the optimal 10% NM-101(Fe)/ZIS can remove 94% of Cr(VI) in 60 min under neutral circumstances, the apparent rate constant is 24.6 and 3.26 times that of NM-101(Fe) and ZIS, respectively. This is due to the hierarchical 0D/3D heterostructure and the unique S-scheme photogenerated carrier transfer path, which successfully encourage the separation of photogenerated carriers while simultaneously enhancing redox ability. Specially, an efficient photo-Fenton-like system was developed using Fe3+ in NM-101(Fe) in conjunction with external H2O2 for entirely eliminating the refractory 2-nitrophenol pollutant in 120 min. It has an apparent rate constant that is 5.63 and 3.99 times that of pure NM-101(Fe) and ZIS. In order to better meet the demands of practical wastewater treatment, the impact of various photocatalyst doses, initial solution concentrations, coexisting ions and pH values on its photocatalytic activity were investigated. Finally, this work provides an idea to construct unique 0D/3D S-scheme heterostructure and effective photo-Fenton-like system for photocatalytic water purification.

All solid-state fabrication strategy of CdS@ZnS nanocomposites and their photocatalytic performance in water purification

Herein a systematic study of two-step solid-phase synthesis of CdS@ZnS nanocomposites and their photocatalytic activity is presented. First, CdS nanoparticles were synthesized in a planetary ball mill through a solid-state ion exchange reaction. In the second step, Cd2+ ions were partially replaced by Zn2+ ions at the surface of the nanoparticles using solvent free long-term activation in a high-energy planetary ball mill. The optimal activation time in a ball mill was determined to be 45 min. Spherical CdS nanoparticles with a diameter of 10 nm and modified CdS@ZnS (45 min) nanocomposites were characterized by X-ray diffraction analysis, Raman and UV-vis spectroscopy, and scanning electron microscopy. The ability of nanocomposites for photocatalytic water purification was tested on the degradation of the model organic dye Orange II in an aqueous solution under the visible light irradation. The modified CdS@ZnS nanocomposites showed higher photocatalytic activity compared to the original CdS nanoparticles.

Self-activated superhydrophilic green ZnIn2S4 realizing solar-driven overall water splitting: close-to-unity stability for a full daytime

Engineering an efficient semiconductor to sustainably produce green hydrogen via solar-driven water splitting is one of the cutting-edge strategies for carbon-neutral energy ecosystem. Herein, a superhydrophilic green hollow ZnIn2S4 (gZIS) was fabricated to realize unassisted photocatalytic overall water splitting. The hollow hierarchical framework benefits exposure of intrinsically active facets and activates inert basal planes. The superhydrophilic nature of gZIS promotes intense surface water molecule interactions. The presence of vacancies within gZIS facilitates photon energy utilization and charge transfer. Systematic theoretical computations signify the defect-induced charge redistribution of gZIS enhancing water activation and reducing surface kinetic barriers. Ultimately, the gZIS could drive photocatalytic pure water splitting by retaining close-to-unity stability for a full daytime reaction with performance comparable to other complex sulfide-based materials. This work reports a self-activated, single-component cocatalyst-free gZIS with great exploration value, potentially providing a state-of-the-art design and innovative aperture for efficient solar-driven hydrogen production to achieve carbon-neutrality.

High-throughput experimentation for photocatalytic water purification in practical environments

High-throughput screening instrument was developed for photocatalytic water purification, enabling the simultaneous testing of 132 photocatalytic reactions under uniform visible light irradiation, temperature control, and stirring. The instrument was used to investigate the effects of different catalysts (TiO2, ZnO, α-Fe2O3) and environmental waters (seawater, urban wastewater, and industrial wastewater) on dye degradation. It was observed environmental ions, particularly carbonate and phosphate ions, significantly reduced catalyst activity by inhibiting the adsorption of dye molecules. To develop effective catalysts for dye degradation in industrial wastewater, 15 types of noble metal nanoparticles (NPs) were supported on photocatalysts. The study found that noble metal NPs with high work functions and oxidation resistance, such as Au and Pt, exhibited higher activity even in the industrial wastewater, likely converting environmental ions into active species. These findings, based on 432 test results, demonstrate the effectiveness of the developed high-throughput screening instrument for optimizing photocatalytic water purification.

P-doped Mn0.5Cd0.5S coupled with cobalt porphyrin as co-catalyst for the photocatalytic water splitting without using sacrificial agents

Photocatalytic water splitting over semiconductors is an important approach to solve the energy demand of human beings. Most photocatalytic H2 generation reactions are conducted in the presence of sacrificial agent. However, the use of sacrificial reagents increases the cost of hydrogen generation. Realizing photocatalytic water splitting for hydrogen production without the addition of sacrificial agents is a major challenge for photocatalysts. The porphyrin MTCPPOMe and P doped MnxCd1-xS make a significant contribution in facilitating the MnxCd1-xS photocatalytic pure water splitting to H2 reaction. Herein, a novel MTCPPOMe/P-MnxCd1-xS (M = 2H, Fe, Co, Ni) composite catalyst which can efficiently split pure water without using sacrificial agents is developed. As a result, the H2 generation rate of CoTCPPOMe/P-Mn0.5Cd0.5S is as high as 2.10 μmol h−1, which is 9.1 and 4.2 times higher than that of Mn0.5Cd0.5S (MCS) and P-Mn0.5Cd0.5S (P-MCS), respectively. P doped MnxCd1-xS inhibits the recombination of photogenerated carriers, and introduction of MTCPPOMe as co-catalyst enhances the reduction capacity. In summary, an efficient and economical photocatalystis prepared for pure water splitting to prepare hydrogen.

Enhanced photocatalytic N2 fixation and water purification using Bi/ZnSnO3 composite: Mechanistic insights and novel applications

A composite of cheap metallic Bi-decorated ZnSnO3 was synthesized via a solvothermal method and applied for photocatalytic N2 fixation for the first time. The results demonstrated that the Bi/ZnSnO3 composite with 1.5 % Bi exhibited superior photocatalytic performance. with the optimal sample producing NH3 at a rate of 988 μmol/L g-1h−1 under simulated sunlight. This is 5 times faster than that of pure ZnSnO3. Additionally, the Bi/ZnSnO3 composite showed significantly better photocatalytic performance than pure ZnSnO3 in RhB degradation. Structural analyses confirmed successful loading of Bi nanoparticles on the surface of ZnSnO3. Furthermore, diffuse reflectance spectroscopy analysis revealed that the surface plasmon resonance effect of metal Bi effectively improved the optical absorption performance. However, the sensitization of metal Bi had a limited contribution to the high photocatalytic activity of the Bi/ZnSnO3. Electrochemical analyses indicated that the Schottky barrier formed between Bi and ZnSnO3 captured photo-generated electrons and promoted the charge separation, which was considered responsible for the increased photoactivity of Bi/ZnSnO3.This work provides a new application of Bi/ZnSnO3 and may offer new ideas for the application of ZnSnO3 materials in the field of photocatalysis, which are crucial for addressing environmental pollution and energy conversion challenges.

Distinctive graphdiyne coupled with phosphorylation NiFe-LDH S-scheme heterojunction for photocatalytic overall water splitting

Most of the photocatalytic reactions currently involved require the use of precious metals or sacrificial reagents to achieve more desirable reactivity and stability. It is urgent to find low-cost photocatalysts that can be stable overall pure water splitting with high efficiency. Graphdiyne (GDY), as the youngest member of the carbon family, has received extensive attention in numerous fields. Herein, the innovative strategy of S-scheme heterojunction composite photocatalysts use to heterogeneous catalysis produce of H2 and H2O2 from photocatalytic pure water splitting is designed using of graphdiyne (GDY) and phosphorylation NiFe layered double hydroxide (NiFe-P). The electron transfer mechanism of S-scheme heterojunction catalyst was verified with in-situ irradiation X-ray photoelectron spectroscopy and hydroxyl radical capture experiments. Achieving multiphase catalysis in pure water, the hydrogen production rate reached 928 μmol h-1g−1, and the H2O2 production rate reached 674 μmol h-1g−1. This work provides new effective scheme for studying the charge transfer pathway of S-scheme heterojunction and feasible methods for constructing efficient photocatalytic-driven pure water splitting reactions.

Modulating charge centers and vacancies in P-CoNi loaded phosphorus-doped ZnIn2S4 nanosheets for H2 and H2O2 photosynthesis from pure water

Photocatalytic water splitting has recently attracted increasing interests for solar to chemical energy conversion. Nevertheless, the high-efficiency process for photocatalytic water splitting is driven by recombination of photogenerated electron-hole pairs and the resultant low H2 productivity. Herein, we demonstrate that P-doping induced positive charge centers (Pδ+) and indium vacancies (VIn) in ZnIn2S4 (ZIS) nanosheets can significantly promote photosplitting pure water to simultaneously produce H2 and H2O2. Microstructural and spectroscopic analysis suggest that Pδ+ and VIn can trap photogenerated electrons and holes, respectively, as a result of enhanced separation of electron-hole pairs. The optimal catalyst of P-CoNi/ZIS displays a stoichiometric H2 and H2O2 productivity of 1228.7 and 1105.5 μmol h−1 g−1, respectively, with an apparent quantum efficiency of 6.2% at 365 nm. Impressively, H2 productivity of P-CoNi/ZIS has surpassed most reported catalysts for photocatalytic pure water splitting. This work provides a unique strategy to create efficient photocatalyst for pure water splitting.

Magnetic Carbon Quantum Dots/Iron Oxide Composite Based on Waste Rice Noodle and Iron Oxide Scale: Preparation and Photocatalytic Capability.

To provide an economical magnetic photocatalyst and introduce an innovative approach for efficiently utilizing discarded waste rice noodle (WRN) and iron oxide scale (IOS), we initially converted WRN into carbon quantum dots (CQDs) using a hydrothermal method, simultaneously calcining IOS to obtain iron oxide (FeOx). Subsequently, we successfully synthesized a cost-effective, magnetic CQDs/FeOx photocatalytic composite for the first time by combining the resulting CQDs and FeOx. Our findings demonstrated that calcining IOS in an air atmosphere enhanced the content of photocatalytically active α-Fe2O3, while incorporating WRN-based CQDs into FeOx improved the electron-hole pair separation, resulting in increased O2 reduction and H2O oxidation. Under optimized conditions (IOS calcination temperature: 300 °C; carbon loading: 11 wt%), the CQDs/FeOx composite, utilizing WRN and IOS as its foundation, exhibited exceptional and reusable capabilities in photodegrading methylene blue and tetracycline. Remarkably, for methylene blue, it achieved an impressive degradation rate of 99.30% within 480 min, accompanied by a high degradation rate constant of 5.26 × 10-3 min-1. This composite demonstrated reusability potential for up to ten photocatalytic cycles without a significant reduction in the degradation efficiency, surpassing the performance of IOS and FeOx without CQDs. Notably, the composite exhibited strong magnetism with a saturation magnetization strength of 34.7 emu/g, which enables efficient and convenient recovery in photocatalytic applications. This characteristic is highly advantageous for the large-scale industrial utilization of photocatalytic water purification.

A review of visible light active SnS photocatalyst for efficient photocatalytic water purification

Due to the complexity of the existing treatment process, illegally releasing chemical-laden wastewater into the nearby rivers and lakes has become the cheapest way for textile dying factories to dispose of it. The untreated harmful synthetic textile dyes released into natural water bodies has created irrecoverable environmental problems and health hazards in several parts of the world. Degradation and complete mineralization of these dyes present in real wastewater are still challenging, due to the presence of several other contaminants. This comprehensive review gives a brief overview of the actual textile effluent treatment processes such as adsorption, floatation, Fenton treatment, Ozonation presently in use and their limitations. Merits of SnS as a material for practical use in natural solar energy driven photocatalysis of toxic dyes are discussed. Owing to their specific surface area and charge separation capabilities, nanostructures, composites and heterostructures generally shows superior catalytic performance over pristine materials. In this review, SnS based photocatalysts are classified into three different categories, namely: nanoparticles and structures, nanocomposites and heterostructures for better comparison of their catalytic performance analysis of the reported results. In each category, the focus of the current review is strategies employed to suppress the reaped recombination, efficient charge transfer mechanism, the relation between morphology and catalytic activity etc. Catalytic performance tables are provided for quick assessment of performance of various materials based on testing conditions. Finally, limitations of the present investigations, different challenges associated with the scale-up process of SnS based visible light photocatalyst and future research directions addressing those challenges are discussed. It is concluded that, by considering the ability to absorb visible light, low-cost, non-toxicity, re-usability and chemical stability, SnS nanostructures, composites and heterostructure catalysts can offer a breakthrough in treating real dye contaminated wastewater.

Few‐Layer Fullerene Network for Photocatalytic Pure Water Splitting into H2 and H2O2

AbstractA few‐layer fullerene network possesses several advantageous characteristics, including a large surface area, abundant active sites, high charge mobility, and an appropriate band gap and band edge for solar water splitting. Herein, we report for the first time that the few‐layer fullerene network shows interesting photocatalytic performance in pure water splitting into H2 and H2O2 in the absence of any sacrificial reagents. Under optimal conditions, the H2 and H2O2 evolution rates can reach 91 and 116 μmol g−1 h−1, respectively, with good stability. This work demonstrates the novel application of the few‐layer fullerene network in the field of energy conversion.

Few-Layer Fullerene Network for Photocatalytic Pure Water Splitting into H2 and H2 O2.

A few-layer fullerene network possesses several advantageous characteristics, including a large surface area, abundant active sites, high charge mobility, and an appropriate band gap and band edge for solar water splitting. Herein, we report for the first time that the few-layer fullerene network shows interesting photocatalytic performance in pure water splitting into H2 and H2 O2 in the absence of any sacrificial reagents. Under optimal conditions, the H2 and H2 O2 evolution rates can reach 91 and 116 μmol g-1 h-1 , respectively, with good stability. This work demonstrates the novel application of the few-layer fullerene network in the field of energy conversion.

Nanorobot-Mediated Synchronized Neuron Activation.

Interactions between active materials lead to collective behavior and even intelligence beyond the capability of individuals. Such behaviors are prevalent in nature and can be observed in animal colonies, providing these species with diverse capacities for communication and cooperation. In artificial systems, however, collective intelligence systems interacting with biological entities remains unexplored. Herein, we describe black (B)-TiO2@N/Au nanorobots interacting through photocatalytic pure water splitting-induced electrophoresis that exhibit periodic swarming oscillations under programmed near-infrared light. The periodic chemical-electric field generated by the oscillating B-TiO2@N/Au nanorobot swarm leads to local neuron activation in vitro. The field oscillations and neurotransmission from synchronized neurons further trigger the resonance oscillation of neuron populations without synaptic contact (about 2 mm spacing), in different ways from normal neuron oscillation requiring direct contact. We envision that the oscillating nanorobot swarm platforms will shed light on contactless communication of neurons and offer tools to explore interactions between neurons.

Cu-Doped Porous ZnO-ZnAl2O4 Nanocomposites Synthesized by Polymer-Salt Method for Photocatalytic Water Purification

In this work, the adsorption and photocatalytic properties of ZnO-ZnAl2O4-CuO nanosized porous composites synthesized by the polymer-salt method have been studied. To evaluate the efficiency of adsorption, experiments were carried out on the decolorization of aqueous solutions of the Chicago Sky Blue diazo dye. The adsorption process is divided into two stages, at the first stage, the dye is rapidly adsorbed on the outer surface of the composite particles (kf = 0.0073 min−1), at the second stage, the dye diffuses into the pores of the material (kf = 0.0007 min−1). It was noted that the rate of photocatalytic decomposition of the dye (kf = 0.021 min−1) is higher than the rate of the adsorption process, which indicates the occurrence of photocatalytic decomposition of dye molecules both on the surface of the composites and in the liquid phase. With an increase in the light intensity, the photocatalytic process is significantly accelerated, linearly at low intensities, and at high intensities (I > 100 mW/cm2) the dependence becomes a power law.

Sulfur-doped Sn3O4 nanosheets for improved photocatalytic performance

Sn3O4 has shown great potential in photocatalytic water purification and energy conversion. However, it is still suffering from limited visible light-harvesting ability and sluggish charge-carrier separation. Nonmetal heteroatom doping is considered as an effective strategy to regulate the electronic structure and improve the photocatalytic performance. Herein, S-doped Sn3O4 was synthesized by a simple hydrothermal method using L-cysteine as sulfur source. It was found that the hierarchical flower-like structure of Sn3O4 would be destructed gradually by sulfur (S) doping. Nevertheless, the as-obtained S(1%)-doped Sn3O4 exhibits remarkable improved photocatalytic degradation performance of azo-dye methyl orange (MO) and antibiotic metronidazole (MTZ). S doped on the lattice of Sn3O4 can narrow the band bap to enhance sufficient photoadsorption, facilitate separating the charge carriers and producing the predominant active species (O2·-) compared with pristine Sn3O4 photocatalyst, resulting in the enhancement of MO/MTZ photogradation activity. This work demonstrates a simple route for S doping in Sn3O4 and provide guidance for the controllable design and synthesis of high-efficient photocatalysts by nonmetal heteroatom doping.