Highly ordered TiO2 nanotube arrays wrapped with g-C3N4 nanoparticles for efficient charge separation and increased photoelectrocatalytic degradation of phenol

Enhanced 1,2-dichloroethane removal using g-C3N4/Blue TiO2 nanotube array photoanode in microbial photoelectrochemical cells

The compound 1,2-dichloroethane (1,2-DCA), a persistent and ubiquitous pollutant, is often found in groundwater and can strongly affect the ecological environment. However, the extreme bio-impedance of C-Cl bonds means that a high energy input is needed to drive biological dechlorination. Biotechnology techniques based on microbial photoelectrochemical cell (MPEC) could potentially convert solar energy into electricity and significantly reduce the external energy inputs currently needed to treat 1,2-DCA. However, low electricity-generating efficiency at the anode and sluggish bioreaction kinetics at the cathode limit the application of MPEC. In this study, a g-C3N4/Blue TiO2-NTA photoanode was fabricated and incorporated into an MPEC for 1,2-DCA removal. Optimal performance was achieved when Blue TiO2 nanotube arrays (Blue TiO2-NTA) were loaded with graphitic carbon nitride (g-C3N4) 10 times. The photocurrent density of the g-C3N4/Blue TiO2-NTA composite electrode was 2.48-fold higher than that of the pure Blue TiO2-NTA electrode under light irradiation. Furthermore, the MPEC equipped with g-C3N4/Blue TiO2-NTA improved 1,2-DCA removal efficiency by 45.21% compared to the Blue TiO2-NTA alone, which is comparable to that of a microbial electrolysis cell. In the modified MPEC, the current efficiency reached 69.07% when the light intensity was 150 mW cm-2 and the 1,2-DCA concentration was 4.4 mM. The excellent performance of the novel MPEC was attributed to the efficient direct electron transfer process and the abundant dechlorinators and electroactive bacteria. These results provide a sustainable and cost-effective strategy to improve 1,2-DCA treatment using a biocathode driven by a photoanode.

TiO2 nanotube arrays-based photoelectrocatalyst: Tri-Doping engineering and carbon coating engineering boosting visible activity, and stable hydrogen evolution

The integration of non-metallic doping and carbon coating for TiO2-based photoelectrocatalysts can be recognized as a promising strategy to enhance their hydrogen production performance. To this end, this study explored the carbon coating engineering to induce stable multi-element doping with an aim to develop high-performance TiO2 nanotube array-based photoelectrocatalysts. The resulting structures consisted of carbon-nitrogen-sulfur-tri-doped TiO2 nanotube arrays with a nitrogen-sulfur-codoped carbon coating (CNS-TNTA/NSC). The fabrication process involved a one-step, low-cost strategy of the carbon-coated tridoped reaction confined in vacuum space, utilizing polymer thiourea sealed in a controlled environment. Compared the photocurrent density of CNS-TNTA/NSC with pristine TNTA, the photocurrent enhancement of approximately 18.3-fold under simulated sunlight and a remarkable increase of 32.8-fold under simulated visible light conditions. The enhanced photocatalytic activity under visible light was ascribed to two factors: First, C, N, and S tri-doping and Ti3+ created a diverse array of impurity energy levels within the band gap, which synergistically narrowed the band gap and further enhanced response to the visible light range. Second, the presence of a carbon coating shell doped with N and S can greatly promote electron transfer and efficient electron-hole pair separation. This study could provide significant insights concerning the design of sophisticated photoanodes.

Biohybrid Urchin-Like ZnO-Based Microspheres with Tunable Hierarchical Structures and Enhanced Photoelectrocatalytic Properties

Microorganisms have attracted much attention to act as biotemplates for fabricating micro/nanostructured functional particles. However, it is still challenging to produce tunable hierarchical particles based on microorganisms with intricate architectures and superior stability. Herein, a novel strategy is developed to fabricate biohybrid urchin-like magnetic ZnO microspheres based on Chlorella (Ch.) with tunable hierarchical core-shell structures. Using Ch. cells as microspherical templates, Fe3 O4 nanoparticles and ZnO nanorod (NR) arrays are deposited in sequence to form the final biohybrid heterostructure microspheres (Ch.@Fe3 O4 @ZnO NRs). Ordered growth and structural regulation of 3D ZnO NR arrays are achieved via a facile and controllable manner. Compared with the prepared microspheres with diverse structure configurations of ZnO shells, the Ch.@Fe3 O4 @ZnO NRs possess excellent light absorption and photoelectrocatalysis performance toward tetracycline degradation (normalized apparent rate constant, k = 366.3 h-1 g-1 ), which is significantly larger than that of ZnO nanoflower/nanoparticle loaded types. It also proves that the synergistic enhancement of well-oriented ZnO NR arrays, heterojunction structures, and biomass features is the fundamental reason for outstanding photoelectrocatalytic activity. Due to the remarkable stability and versatility, this work provides abundant opportunities to construct biohybrid multilevel micro/nanostructures with significant potentials for practical applications.

Photocatalytic degradation of alkyl imidazole ionic liquids by TiO2 nanospheres under simulated solar irradiation: Transformation behavior, DFT calculations and promoting effects of alkali and alkaline earth metal ions

In this study, TiO2 nanospheres prepared by the sol-gel method were found to efficiently catalyze the photodegradation of 1-butyl-2,3-dimethylimidazolium bromide salt ([BMMIm]Br) under simulated solar irradiation through the main attack of hydroxyl radicals (•OH). The promoting effect of alkali metal (Li+→Cs+) and alkaline earth metal ions (Mg2+→Ba2+) was particularly emphasized. In-situ EPR tests showed that the introduction of alkali and alkaline earth metal ions could enhance the formation of •OH thus leading to a 7%-30.3% increase in the degradation efficiency of. [BMMIm]+. Moreover, the removal efficiency of [BMMIm]+ still reached > 96.19% in four real waters. A total of 23 products of [BMMIm]Br were detected, and hydroxyl substitution, bond breaking, direct oxidation and ring opening were considered as the main reactions during the photocatalytic degradation process. The results of toxicity evaluation showed that hydroxylation was a reaction process of increasing toxicity, while the bond breaking reaction had great detoxification capacity for [BMMIm]+. These findings may enhance our understanding on the effects of alkali or alkaline earth metal ions on the photocatalytic activity of TiO2, which could also provide reference for the efficient and green removal of alkylimidazolium ionic liquids in waters.

Progress in Promising Semiconductor Materials for Efficient Photoelectrocatalytic Hydrogen Production

Photoelectrocatalytic (PEC) water decomposition provides a promising method for converting solar energy into green hydrogen energy. Indeed, significant advances and improvements have been made in various fundamental aspects for cutting-edge applications, such as water splitting and hydrogen production. However, the fairly low PEC efficiency of water decomposition by a semiconductor photoelectrode and photocorrosion seriously restrict the practical application of photoelectrochemistry. In this review, the mechanisms of PEC water decomposition are first introduced to provide a solid understanding of the PEC process and ensure that this review is accessible to a wide range of readers. Afterwards, notable achievements to date are outlined, and unique approaches involving promising semiconductor materials for efficient PEC hydrogen production, including metal oxide, sulfide, and graphite-phase carbon nitride, are described. Finally, four strategies which can effectively improve the hydrogen production rate-morphological control, doping, heterojunction, and surface modification-are discussed.

Design strategies and mechanisms of g-C3N4-based photoanodes for photoelectrocatalytic degradation of organic pollutants in water

Emerging photoelectrocatalytic (PEC) systems integrate the advantages of photocatalysis and electrocatalysis and are considered as a promising technology for solving the global organic pollution problem in water environments. Among the photoelectrocatalytic materials applied for organic pollutant degradation, graphitic carbon nitride (CN) has the combined advantages of environmental compatibility, stability, low cost, and visible light response. However, pristine CN has disadvantages such as low specific surface area, low electrical conductivity, and high charge complexation rate, and how to improve the degradation efficiency of PEC reaction and the mineralization rate of organic matter is the main problem faced in this field. Therefore, this paper reviews the progress of various functionalized CN used for PEC reaction in recent years, and the degradation efficiency of these CN-based materials is critically evaluated. First, the basic principles of PEC degradation of organic pollutants are outlined. Then, engineering strategies to enhance the PEC activity of CN (including morphology control, elemental doping, and heterojunction construction) are focused on, and the structure-activity relationships between these engineering strategies and PEC activity are discussed. In addition, the important role of influencing factors on the PEC system is summarized in terms of mechanism, to provide guidance for the subsequent research. Finally, suggestions and perspectives are provided for the preparation of efficient and stable CN-based photoelectrocatalysts for practical wastewater treatment applications.

Dual-modification strategy of Co(II) and g-C3N4 to CuS for efficient colorimetric determination of thioglycolic acid in daily cosmetics

A conventional colorimetric method based on CuS-catalyzed H₂O₂ is improved by a dual-modification strategy and employed for thioglycolic acid (TGA) determination. The doping of Co(II) can enhance ion exchange efficiency. Meanwhile, the modification of g-C₃N₄ can increase specific surface area and decrease unspecific aggregation. The constructed g-C₃N₄/Co-CuS nanocomposite exhibited a favorable catalytic feature. A Michaelis constant (K_m) value of 0.02 mM has been achieved, which is 1/160 of those of CuS and horseradish peroxidase (HRP). The g-C₃N₄/Co-CuS displays a rapid color response in 3 min and resulted in a stable measurable signal within 10 min. In the determination procedure, the sulfhydryl contained in TGA is capable of preventing TMB oxidation via competing the ·OH produced by catalysis and caused a color distinction that is related to the TGA amount. The distinctions of absorbance (λ_max = 652 nm) of different concentrations of TGA are recorded. Linearity is obtained in the ranges of 2.5 - 20 µM and 20 - 160 µM, and the LOD is 0.14 µM. In the real sample assays of perm agent and Qianhu lake water, the recoveries were 96.70 - 106.84% and 100.21 - 101.90%, respectively. This demonstrates that the proposed dual-modification strategy for CuS contributes to highly efficient and convenient determination of TGA in daily cosmetics and water analysis.

TiO2 nanoparticles modified graphitic carbon nitride with potential-resolved multicolor electrochemiluminescence and application for sensitive sensing of rutin

Recently, nanocomposites with potential-resolved multicolor electrochemiluminescence (ECL) property have attracted new research interests. Herein, TiO₂ nanoparticles modified graphitic carbon nitride (TiO₂-NPs/g-C₃N₄) with inherent potential-resolved multicolor ECL emission was prepared via a simple synthesis method. The morphology and chemical composition of the synthesized TiO₂-NPs/g-C₃N₄ were characterized. The obtained TiO₂-NPs/g-C₃N₄ exhibited dual-peak multicolor ECL emission under cyclic voltammetry scanning by using K₂S₂O₈ as co-reagent. The first ECL peak (ECL-1) is composed of turquoise blue ECL emission (471 nm) located at -1.3 V and olive green ECL emission (490 nm) ranging from -1.4 to -2.0 V. The second ECL peak (ECL-2) is composed of navy blue ECL emission (458 nm) located at -3.0 V. The ECL mechanism for the potential-resolved multicolor ECL emission was proposed. Furthermore, the first ECL imaging sensing method was fabricated for the sensitive quantitative detection of rutin based on the effective quenching effect of rutin on the ECL of TiO₂-NPs/g-C₃N₄. The linear response range is 0.005-400 µM with detection limit as low as 2 nM. This work presents a simple way to prepare g-C₃N₄-based nanocomposites with potential-resolved multicolor ECL, which broadens the potential applications of g-C₃N₄-based nanocomposites for ECL imaging sensing and light-emitting devices.

Pt-N Co-Modified TiO2 Nanotube Electrode Photoelectrocatalytic Degradation of Oxytetracycline in Simulated Wastewater

Using photodeposition and plasma, Pt-N co-modified TiO₂ nanotube electrodes were created. Several techniques, such as SEM, XRD, UV-VIS-DRS, XPS, and PL, were used to analyze the electrode shape, crystalline structure, light absorption range, elemental composition, and photogenerated carrier recombination efficiency. Using the electrochemical workstation, EIS and I-t were utilized to examine the electrochemical characteristics. The results indicated that the diameter of the TiO₂ nanotube tubes was around 90 nm, and that the photodeposition duration affected the amount of Pt particles deposited. The deposited Pt particles efficiently reduced the photogenerated carrier complexation rate of the N-TiO₂ nanotube electrode, contributing to the separation of electron-hole pairs and light utilization. Electrochemical studies indicated that Pt-N co-modified TiO₂ increased the electrode's oxidation and electrical conductivity, as well as its photoelectrocatalytic capacity. Oxytetracycline degradation in simulated wastewater by a Pt-N co-modified TiO₂ nanotube electrode revealed the exceptional PEC activity, and the oxytetracycline degradation processes followed primary kinetics. •O₂^- and •OH played a significant role in the photoelectrocatalytic degradation of oxytetracycline, resulting in a novel method for oxytetracycline degradation.

Exploring the visible light-assisted conversion of CO2 into methane and methanol, using direct Z-scheme TiO2@g-C3N4 nanosheets: synthesis and photocatalytic performance

The rapid growth of carbon dioxide (CO₂) emissions raises concern about the possible consequences of atmospheric CO₂ increase, such as global warming and greenhouse effect. Photocatalytic CO₂ conversion has attracted researchers' interests to find a sustainable route for its elimination. In the present study, a direct Z-scheme TiO₂/g-C₃N₄ composite (T-GCN) was fabricated via a facile hydrothermal route for the photocatalytic reduction of CO₂ into methane (CH₄) and methanol (CH₃OH), under visible light irradiation without an electron mediator. The microstructure of the as-obtained TiO₂/g-C₃N₄ nanocomposites was fully characterized for its physicochemical, structural, charge separation, electronic, and photo-excited carrier separation properties. The effect of CO₂ and H₂O partial pressure was studied to find the best operational conditions for obtaining maximum photocatalytic efficiency; the P_CO2 and P_H2O were 75.8 and 15.5 kPa, respectively, whereas, by increasing the light intensity from 20 to 80 mW/cm², a remarkable improvement in the reduction rate takes place (from 11.04 to 32.49 μmol.gcat^-1.h^-1 methane production, respectively). Finally, under the most favorable light, P_CO2 and P_H2O conditions, high methanol and methane rates were obtained from the CO₂ photocatalytic reduction through T-GCN (1.44 μmol.gcat.^-1.h^-1 and 32.49 μmol.gcat.^-1.h^-1, respectively) and an integrated proposition for the Z-scheme mechanism of photocatalytic reduction was proposed. This study offers a promising strategy to synthesize a Z-scheme T-GCN heterojunction with high photocatalytic performance for effective CO₂ conversion.

Bismuth Oxyhalide-Based Materials (BiOX: X = Cl, Br, I) and Their Application in Photoelectrocatalytic Degradation of Organic Pollutants in Water: A Review

An important target of photoelectrocatalysis (PEC) technology is the development of semiconductor-based photoelectrodes capable of absorbing solar energy (visible light) and promoting oxidation and reduction reactions. Bismuth oxyhalide-based materials BiOX (X = Cl, Br, and I) meet these requirements. Their crystalline structure, optical and electronic properties, and photocatalytic activity under visible light mean that these materials can be coupled to other semiconductors to develop novel heterostructures for photoelectrochemical degradation systems. This review provides a general overview of controlled BiOX powder synthesis methods, and discusses the optical and structural features of BiOX-based materials, focusing on heterojunction photoanodes. In addition, it summarizes the most recent applications in this field, particularly photoelectrochemical performance, experimental conditions and degradation efficiencies reported for some organic pollutants (e.g., pharmaceuticals, organic dyes, phenolic derivatives, etc.). Finally, as this review seeks to serve as a guide for the characteristics and various properties of these interesting semiconductors, it discusses future PEC-related challenges to explore.

O-Fluorobenzoic Acid-Mediated Construction of Porous Graphitic Carbon Nitride with Nitrogen Defects for Multicolor Electrochemiluminescence Imaging Sensing

Graphitic carbon nitride (g-CN) is an attractive electrochemiluminescence (ECL) luminophore. However, g-CN with wavelength-tunable ECL emission is still limited, which limits its application in multicolor ECL sensing and imaging analysis. In this study, porous g-CN (PCN) with nitrogen defects was synthesized through the condensation of melamine by using o-fluorobenzoic acid (o-FBA) as an effective regulation reagent. A series of PCNs, including PCN-5%, PCN-10%, and PCN-30%, were obtained by changing the mass ratio of o-FBA and melamine. The porous structure and tunable chemical composition change of the PCNs were carefully characterized. The nitrogen defects and porous structure of the synthesized PCNs can enlarge the specific surface area, facilitate electron transfer, and generate various surface states with gradually changed energy bands, leading to wavelength-tunable multicolor ECL emissions. Accordingly, g-CN, PCN-5%, PCN-10%, and PCN-30% can generate navy blue, turquoise blue, turquoise green, and olive green ECL emissions, respectively, with the peak ECL wavelength varied from 465 to 550 nm. Then, a multicolor ECL sensing array was proposed for the discrimination of polyphenols based on the prepared g-CN and PCNs by using a smartphone as a portable detector for the first time. Five polyphenol substances including vitamin P, resveratrol, phloretin, phlorizin, and caffeic acid were discriminated by using principal component analysis and hierarchical cluster analysis. The present work provides a simple strategy to adjust the ECL wavelength of g-CN and presents a simple way to fabricate multicolor ECL sensing array, which has great application potential for multiplexed analysis and multicolor ECL imaging sensing.

0D/3D NiCo2O4/defected UiO-66 catalysts for enhanced degradation of tetracycline in peroxymonosulfate/simulated sunlight systems: Degradation mechanisms and pathways

Developing synergistic systems and taking environmental risks into account are two necessary aspects of being considered to remove persistent organic pollutants efficiently. Thus, a combined catalytic system uniting the Fenton-like process and simulated solar-light photocatalysis has been constructed. Moreover, a series of NiCo₂O₄/HP-UiO-66 catalysts (yNiCo-DUx) were also fabricated to improve tetracycline (TC) removal efficiency. The NiCo₂O₄ nanoparticles (NPs) and hierarchically porous metal-organic frameworks (HP-MOFs) were synthesised using one-step calcination. The Z-scheme structure of the catalysts was confirmed by ESR, XPS, DRS, time-resolved PL (TR-PL) spectra and the quenching experiments. The NiCo₂O₄ nanoparticles could be embedded and fixed into the defects of the MOF structure, and the leaching of toxic metals was also significantly suppressed. In the optimal reaction condition with 15NiCo-DU50, sunlight, and peroxymonosulfate (PMS), the total removal efficiency of TC could reach 98.5% within 8 min of irradiation, and the highest % RSE could reach 11.2%. Moreover, the corresponding reaction rate was 28.7, 3.6 and 1.3-10.2 times higher than photocatalysis, Fenton-like processes and other catalysts. Furthermore, the possible degradation mechanism, generation of reactive species and PMS excitation pathways were also investigated in depth. The present study sheds light on the fabrication of HP-MOFs based catalysts and the combination of various methods to eliminate organic pollutants.

Application of Composite Film Containing Polyoxometalate Ni25 and Reduced Graphene Oxide for Photoelectrocatalytic Water Oxidation

The preparation of clean energy is an effective way to solve the global energy crisis and reduce environmental pollution. The decomposition of water can produce hydrogen and oxygen, which is one of the effective ways to prepare clean energy. However, water oxidation is a bottleneck for water decomposition, thus, developing a water oxidation catalyst can accelerate the process of water decomposition to generate clean energy. Nickel-substituted polyoxometalate [Ni25(H2O)2(OH)18(CO3)2(PO4)6(SiW9O34)6]50− (Ni25) is proven as an excellent water oxidation photocatalyst. To develop the effective photoelectrocatalyst for water oxidation, in this work, we constructed two composite films containing Ni25 on ITO, [PDDA/Ni25]n, and PDDA/[Ni25/(PDDA–rGO)]n, by layer-by-layer self-assembly, which is the first combination of nickel-substituted polyoxometalates and reduced graphene oxide (rGO). The study on the photoelectrocatalytic performance of the two films indicates that the water oxidation current of the film PDDA/[Ni25/(PDDA–rGO)]n-modified electrode is increased by 33.7% after light irradiation, which is 1.71 times that of the film [PDDA/Ni25]n-modified electrode. Moreover, the transient photocurrent response of the film PDDA/[Ni25/(PDDA–rGO)]n-modified electrode demonstrates that there is a synergistic effect between rGO and Ni25, and rGO-accelerated electron transport and inhibited charge recombination. In addition, the film PDDA/[Ni25/(PDDA–rGO)]n-modified electrode exhibits good stability, indicating its great potential as an effective photoelectrocatalyst for water oxidation in practical application.

In situ engineering of highly conductive TiO2/carbon heterostructure fibers for enhanced electrocatalytic degradation of water pollutants

Rational design of nanocomposite electrode materials with high conductivity, activity, and mechanical strength is critical in electrocatalysis. Herein, freestanding, flexible heteronanocomposites were fabricated in situ by carbonizing electrospun fibers with TiO₂ nanoparticles on the surface for electrocatalytic degradation of water pollutants. The carbonization temperature was observed as a dominant parameter affecting the characteristics of the electrodes. As the carbonization temperature increased to 1000 °C, the conductivity of the electrode was significantly enhanced due to the high degree of graphitization (I_D/I_G ratio 1.10) and the dominant rutile phase. Additionally, the formation of TiO₂ protrusions and the C-Ti heterostructure were observed at 1000 °C, which contributed to increasing the electrocatalytic activity. When 1.5 V (vs. Ag/AgCl) was employed, electrocatalytic experiments using the electrode achieved 90% degradation of crystal violet and 10.9-87.5% for an array of micropollutants. The electrical energy-per-order (EEO) for the removal of crystal violet was 0.7 kWh/m³/order, indicative of low-energy requirement. The efficient electrocatalytic activity can be ascribed to the fast electron transfer and the strong ability to generate hydroxyl radicals. Our findings expand efforts for the design of highly conductive heteronanocomposites in a facile in situ approach, providing a promising perspective for the energy-efficient electrocatalytic degradation of water pollutants.

Graphene-derived antibacterial nanocomposites for water disinfection: Current and future perspectives

Antimicrobial nanomaterials provide numerous opportunities for the synthesis of next-generation sustainable water disinfectants. Using the keywords graphene and water disinfection and graphene antibacterial activity, a detailed search of the Scopus database yielded 198 and 1433 studies on using graphene for water disinfection applications and graphene antibacterial activity in the last ten years, respectively. Graphene family nanomaterials (GFNs) have emerged as effective antibacterial agents. The current innovations in graphene-, graphene oxide (GO)-, reduced graphene oxide (rGO)-, and graphene quantum dot (GQD)-based nanocomposites for water disinfection, including their functionalization with semiconductor photocatalysts and metal and metal oxide nanoparticles, have been thoroughly discussed in this review. Furthermore, their novel application in the fabrication of 3D porous hydrogels, thin films, and membranes has been emphasized. The physicochemical and structural properties affecting their antibacterial efficiency, such as sheet size, layer number, shape, edges, smoothness/roughness, arrangement mode, aggregation, dispersibility, and surface functionalization have been highlighted. The various mechanisms involved in GFN antibacterial action have been reviewed, including the mechanisms of membrane stress, ROS-dependent and -independent oxidative stress, cell wrapping/trapping, charge transfer, and interaction with cellular components. For safe applications, the potential biosafety and biocompatibility of GFNs in aquatic environments are emphasized. Finally, the current limitations and future perspectives are discussed. This review may provide ideas for developing efficient and practical solutions using graphene-, GO-, rGO-, and GQD-based nanocomposites in water disinfection by rationally employing their unique properties.

Engineered defect-rich TiO2/g-C3N4 heterojunction: A visible light-driven photocatalyst for efficient degradation of phenolic wastewater

Photocatalytic technology has been considered as an effective way for pollutants removal. Considering that the nature of the photodegradation of pollutants is the free radical reaction on the surface of the catalyst, promoting the generation of free radicals is a direct and effective way to facilitate the mineralization of pollutants. Unfortunately, the shortcomings strongly limit its photocatalytic activity such as insufficient sunlight utilization, small catalytic surface and rapid recombination of charge. Here, a heterostructure of defect-rich TiO₂ nanoparticles anchored in g-C₃N₄ was fabricated by a synchronous compound process. This heterostructure (4TiO₂/g-C₃N₄) exhibits an enhanced visible light absorption due to its narrow band gap energy of 2.27 eV. Therefore, it possesses an outstanding photocatalytic activity for the degradation of phenol (1.63 × 10² μmol g^-1 h^-1), p-nitrophenol (1.15 × 10² μmol g^-1 h^-1), o-cresol (1.43 × 10² μmol g^-1 h^-1) and p-cresol (1.45 × 10² μmol g^-1 h^-1). The calculated quantum yields of 4TiO₂/CN for pollutants degradation are 1.29 × 10^-6 for phenol, 9.10 × 10^-7 for p-nitrophenol, 1.14 × 10^-6 for o-cresol and 1.15 × 10^-6 for p-cresol, respectively. By utilizing the periodic topology of MOFs, this work provides an improved approach for constructing TiO₂/g-C₃N₄ heterojunctions with enhanced degradation of robust organic pollutants.

Advances in application of g-C3N4-based materials for treatment of polluted water and wastewater via activation of oxidants and photoelectrocatalysis: A comprehensive review

Recently, graphitic carbon nitride (g-C₃N₄) has received significant attention as a non-metallic, visible-light-activated photocatalyst for treating water and wastewater by degrading contaminants. Accordingly, previous review articles have focused on the photocatalytic properties of g-C₃N₄-based materials. However, g-C₃N₄ has several other notable features, such as high adsorption affinity towards aromatic substances and heavy metals, high thermal and chemical resistances, good compatibility with various materials, and easily scalable synthesis; therefore, in addition to simple photocatalysis, it can be widely used in other decontamination systems based on activation of oxidants and electrocatalysis. This critical review provides a comprehensive summary of recent advancements in g-C₃N₄-based materials and their use in treating polluted water and wastewater via the following routes (1) activation of oxidizing agents (e.g., hydrogen peroxide, ozone, peroxymonosulfate, and persulfate): and (2) photoelectrocatalysis using fabricated g-C₃N₄-based photocathodes and photoanodes. For each route, we briefly summarize the primary mechanisms, distinctive features, and performances of various water treatment systems using g-C₃N₄-based catalysts. We also highlight the specific roles of g-C₃N₄ in improving the efficiencies of these treatment processes. The advantages and limitations of previously reported water treatment systems using g-C₃N₄-based materials are also described and compared in this review. Finally, we discuss the challenges and prospects of improving g-C₃N₄-based water purification applications.

Efficient mineralization of TBBPA via an integrated photocatalytic reduction/oxidation process mediated by MoS2/SnIn4S8 photocatalyst

Currently, Tetrabromobisphenol A (TBBPA) has been regarded as an emerging organic pollutant and efficient TBBPA elimination technology has been attracting increasing attention. In this work, a novel photocatalyst, MoS₂/SnIn₄S₈, was synthesized through hydrothermal method by introducing few-layer MoS₂ nanosheets and then employed to establish an integrated photocatalytic reduction/oxidation system for the remediation of TBBPA under visible light. The characterization results demonstrated that the few-layer MoS₂ nanosheets were well combined with SnIn₄S₈ and significantly lowered the recombination rate of the photo-induced electron and holes, leading to outstanding photocatalytic performance of MoS₂/SnIn₄S₈ composite. Besides, the MoS₂/SnIn₄S₈ composite also exhibited excellent reusability (over 10 runs) and stability. The TBBPA degradation experiments showed that the integrated photocatalytic reduction/oxidation system was able to completely degrade TBBPA and mineralize its byproducts (60.2 ± 2.9%). In the photocatalytic reduction, due to the cleavage of C-Br bonds by photo-induced electrons, TBBPA underwent stepwise debromination and finally transferred into BPA in 6 h. In the following photocatalytic oxidation, under the attack of reactive oxygen species (¹O₂, h⁺,OH and O₂^-), BPA was first decomposed into aromatic products (such as phenol, benzoic acid, p-hydroxybenzyl alcohol and so on) via C-C bond cracking and hydroxylation, and then further oxidized into organic acids like maleic acid and muconic acid through ring-opening, and finally mineralized into CO₂ and H₂O. What was noteworthy was that the final effluent from the photocatalytic reduction/oxidation system showed no toxicity to the luminescent bacteria.

Synthesis and Photocatalytic Activity of TiO2/CdS Nanocomposites with Co-Exposed Anatase Highly Reactive Facets

In this work, TiO2/CdS nanocomposites with co-exposed {101}/[111]-facets (NH4F-TiO2/CdS), {101}/{010} facets (FMA-TiO2/CdS), and {101}/{010}/[111]-facets (HF-TiO2/CdS and Urea-TiO2/CdS) were successfully synthesized through a one-pot solvothermal method by using [Ti4O9]2- colloidal solution containing CdS crystals as the precursor. The crystal structure, morphology, specific surface area, pore size distribution, separation, and recombination of photogenerated electrons/holes of the TiO2/CdS nanocomposites were characterized. The photocatalytic activity and cycling performance of the TiO2/CdS nanocomposites were also investigated. The results showed that as-prepared FMA-TiO2/CdS with co-exposed {101}/{010} facets exhibited the highest photocatalytic activity in the process of photocatalytic degradation of methyl orange (MO), and its degradation efficiency was 88.4%. The rate constants of FMA-TiO2/CdS was 0.0167 min-1, which was 55.7, 4.0, 3.7, 3.5, 3.3, and 1.9 times of No catalyst, CdS, HF-TiO2/CdS, NH4F-TiO2/CdS, CM-TiO2, Urea-TiO2/CdS, respectively. The highest photocatalytic activity of FMA-TiO2/CdS could be attributed to the synergistic effects of the largest surface energy, co-exposed {101}/{010} facets, the lowest photoluminescence intensity, lower charge-transfer resistance, and a higher charge-transfer efficiency.

Well-designed three-dimensional hierarchical hollow tubular g-C3N4/ZnIn2S4 nanosheets heterostructure for achieving efficient visible-light photocatalytic hydrogen evolution

Photocatalytic water splitting for hydrogen production is an important strategy to achieve clean energy development. In this report, a novel three-dimensional (3D) hierarchical hollow tubular g-C₃N₄/ZnIn₂S₄ nanosheets (HTCN/ZIS) type-Ⅱ heterojunction photocatalyst was successfully prepared and applied for photocatalytic hydrogen production under visible light irradiation. The experimental results reveal that the optimal proportion of HTCN/ZIS with the remarkable photocatalytic H₂ evolution rate of 20738 μmol h^-1 g^-1 was obtained. The main reasons for the improvement of hydrogen production activity are as follows: (i) this unique tubular hollow structure can effectively enhances the light capturing ability by the multiple light scattering/reflection of incident light in the inner cavity; (ii) the shorten the phase plane transmission distance could reduce the path of charge transfer; (iii) the surface coated a large number of scaly ZnIn₂S₄ nanosheets can provide abundant reactive sites. Combining the various characterization tests, the enhanced spatial segregation of charge carriers could owning to the intimately interfacial contact and well-matched band gaps structure between g-C₃N₄ and ZnIn₂S₄ through the type-II heterojunction. This work provides a new prospect for the construction of a novel 3D hierarchical type-II heterojunction photocatalyst for highly efficient photocatalytic hydrogen production.

Highly Efficient Degradation of Persistent Pollutants with 3D Nanocone TiO2-Based Photoelectrocatalysis

Photoelectrocatalytic (PEC) degradation of organic pollutants into CO₂ and H₂O is a promising strategy for addressing ever-growing environmental problems. Titanium dioxide (TiO₂) has been widely studied because of its good performance and environmental benignancy; however, the PEC activity of TiO₂ catalyst is substantially limited due to its fast electron-hole recombination. Herein, we report a TiO₂ nanocone-based photoelectrocatalyst with superior degradation performance and outstanding durability. The unique conical catalyst can boost the PEC degradation of 4-chlorophenol (4-CP) with 99% degradation efficiency and higher than 55% mineralization efficiency at a concentration of 20 ppm. The normalized apparent rate constant of a nanocone catalyst is 5.05 h^-1 g^-1 m², which is 3 times that of a nanorod catalyst and 6 times that of an aggregated particle catalyst, respectively. Further characterizations reveal that the conical morphology of TiO₂ can make photogenerated charges separate and transfer more efficiently, resulting in outstanding PEC activity. Moreover, computational fluid dynamics simulations indicate that a three-dimensional conical structure is beneficial for mass transfer. This work highlights that tuning the morphology of a photoelectrocatalyst at the nanometer scale not only promotes the charge transfer but also facilitates the mass transportation, which jointly enhance the PEC performance in the degradation of persistent pollutants.

Ultrasensitive SERS detection of exhaled biomarkers of lung cancer using a multifunctional solid phase extraction membrane

The construction and clinical application of a surface-enhanced Raman scattering (SERS) platform for the early diagnosis of lung cancer could improve the survival rate of patients and would be of great significance. Nevertheless, a sensitive and reusable method for the detection of aldehydes, as biomarkers of lung cancer, in exhaled breath is still an enormous challenge. Aldehydes generally have a low cross section in Raman scattering and have a weak specific affinity to plasmonic nanoparticle surfaces, meaning that sensing them at low concentrations is incredibly difficult. Herein, an ultrasensitive SERS strategy, that can be recycled for further use, for the detection of lung cancer biomarkers in the form of aldehydes was realized by fabrication of a multifunctional Ag NPs@ZIF-67/g-C₃N₄ solid phase extraction (SPE) membrane. Based on the change in the vibrational fingerprints of 4-ATP before and after reaction with the aldehydes, the SPE membrane was successfully used for the ultrasensitive detection of aldehydes with a detection limit of 1.35 nM. The excellent SERS performance was attributed to the synergistic effect of the densely and closely distributed Ag NPs (providing SERS "hot spots"), ZIF-67 (concentrating the analyte molecules) and g-C₃N₄ (forming a membrane to prolong the contact time between the aldehydes and the substrate). In addition, recycling of the SPE membrane was achieved by utilizing the self-cleaning ability of the Ag NPs@ZIF-67/g-C₃N₄ membrane originating from the photocatalytic properties of g-C₃N₄. The proposed SERS membrane was easy to operate, rapid and portable, thus providing a potential tool for a point-of-care test in clinical and diagnostic practice.

Photoelectrocatalytic degradation of p-chloronitrobenzene by g-C3N4/TiO2 nanotube arrays photoelectrodes under visible light irradiation

As a typical refractory pollutant, p-chloronitrobenzene (p-CNB) from industrial wastewater poses a serious threat to the aquatic environment safety and human health. The photoelectrocatalytic (PEC) technology is regarded as a promising and cleaner approach for p-CNB removal. Therefore, the graphitic carbon nitride (g-C₃N₄) modified TiO₂ nanotube arrays (g-C₃N₄/TNAs) were prepared as the photoelectrodes for p-CNB degradation. The PEC degradation efficiency for p-CNB by g-C₃N₄/TNAs (0.00484 min^-1) was much higher than that by bare TNAs (0.00135 min^-1) under visible light. The g-C₃N₄/TNAs photoelectrodes exhibited excellent visible-light response, efficient charges separation and high redox potentials of electron/hole, which was favorable for p-CNB degradation. The radical scavenging experiments indicated that both reductive electrons and oxidized species (holes and ·OH) played crucial roles simultaneously during the dechlorination process, whereas the mineralization of p-CNB mainly depended on the photo-generated holes and ·OH. The degradation pathways of p-CNB were proposed through GC/MS spectra. The acute toxicity, bioaccumulation factor and mutagenicity of identified intermediates were reduced after PEC degradation by g-C₃N₄/TNAs photoelectrodes. The Z-scheme g-C₃N₄/TNAs provided an efficient approach for simultaneous dechlorination and mineralization of refractory pollutants.

Enhancement of visible light driven dye degradation and photocatalytic H2 evolution over MoS2 through combination with perylene diimide aggregates

The incorporation of PPDI MBs into MoS₂ NFs changes the nature of their edge, increases the driving force to effectively separate and transfer the photogenerated charge carriers, and improves the overall photocatalytic performance of the material.

Fabrication and high photoelectrocatalytic activity of scaly BiOBr nanosheet arrays

Bismuth oxybromide (BiOBr) nanosheet arrays (NSAs) were successfully prepared on the surface of indium tin oxide glass (hydrophilic pretreated) by solvothermal method using [C₁₆mim]Br ionic liquid as bromine source and template. The effects of different reaction temperatures on array synthesis were investigated. BiOBr NSA-160 (NSAs prepared at 160 °C for 8 h) had the best photoelectrocatalytic (PEC) activity. The removal rate of ciprofloxacin hydrochloride by BiOBr NSA-160 was 91.4% by applying a bias voltage of 0.9 V and irradiating under visible light for 180 min. Results of the analyses of the morphology, photoelectric properties, energy band structure, and degradation active species show that BiOBr NSA-160 is a p-type photocatalyst with a thickness of approximately 500 nm, a light response range of less than 440 nm, and photocurrent density of 69 μA/cm² at the optimal bias voltage is 0.9 V. The high PEC activity of BiOBr NSA-160 was deduced from two aspects: one is that the bias potential effectively improves the separation efficiency of photogenerated carrier, and the other is that the structure of the nanoarray increases light absorption and active sites. BiOBr NSAs are promising PEC material for application in pollutant removal.

Efficient Self-Driving Photoelectrocatalytic Reactor for Synergistic Water Purification and H2 Evolution

The photoelectrocatalytic (PEC) technique has attracted much attention to getting clear energy and environmental purification. Simultaneous reactions of solar energy generation could be used to apply for practical applications to maximize the functionality of reactor systems. Herein, we crafted a self-driving photoelectrocatalytic reactor system, comprising platinum (Pt) modified p-Si nanowires (Pt/Si-NWs) as a photocathode and TiO₂ nanotube arrays (TiO₂-NTAs) as a photoanode for synergistic H₂ evolution and water purification, respectively. Hydrogen evolution in the cathode chamber and environmental remediation in the anode chamber were achieved with the aid of appropriate bandgap illumination and self-built bias voltage. The mismatch of Fermi levels between TiO₂-NTAs and Si-NWs reduced the recombination rates of photoinduced electrons and holes through the formation of Z scheme and inner electric filed. The synergistic PEC reactions exhibited much higher activities than those achieved using other systems so far. This basic principal could be applied for fabricating other PEC reactors in photoelectro conversion devices and be established as design guidelines for reactors to maximize the PEC performance.

Present applications of titanium dioxide for the photocatalytic removal of pollutants from water: A review

The evolution of modern technology and industrial processes has been accompanied by an increase in the utilization of chemicals to derive new products. Water bodies are frequently contaminated by the presence of conventional pollutants such as dyes and heavy metals, as well as microorganisms that are responsible for various diseases. A sharp rise has also been observed in the presence of new compounds heretofore excluded from the design and evaluation of wastewater treatment processes, categorized as "emerging pollutants". While some are harmless, certain emerging pollutants possess the ability to cause debilitating effects on a wide spectrum of living organisms. Photocatalytic degradation has emerged as an increasingly popular solution to the problem of water pollution due to its effectiveness and versatility. The primary objective of this study is to thoroughly scrutinize recent applications of titanium dioxide and its modified forms as photocatalytic materials in the removal and control of several classes of water pollutants as reported in literature. Different structural modifications are used to enhance the performance of the photocatalyst such as doping and formation of composites. The principles of these modifications have been scrutinized and evaluated in this review in order to present their advantages and drawbacks. The mechanisms involved in the removal of different pollutants through photocatalysis performed by TiO2 have been highlighted. The factors affecting the mechanism of photocatalysis and those affecting the performance of different TiO2-based photocatalysts have also been thoroughly discussed, thereby presenting a comprehensive view of all aspects involved in the application of TiO₂ to remediate and control water pollution.

AgInS2 and graphene co-sensitized TiO2 photoanodes for photocathodic protection of Q235 carbon steel under visible light

AgInS₂ nanoparticle and graphene nanosheet co-sensitized anatase TiO₂ nanotube array films were fabricated by a combination of hydrothermal reaction and electrochemical anodization on titanium sheets. The results showed that the co-sensitization of AgInS₂ nanoparticles and graphene nanosheets extended the photoresponse of TiO₂ nanotubes into the visible-light region, and improved the photogenerated charge separation and transfer capability. The photocurrent density of the AgInS₂/graphene/TiO₂ composites (about 4.0 mA cm^-2) was 20 times that of bare TiO₂ (only 0.2 mA cm^-2) under visible-light illumination. The potential negative shift value of AgInS₂/graphene/TiO₂ composites was up to 0.68 V versus saturated calomel electrode. The AgInS₂/graphene/TiO₂ composites can provide Q235 carbon steel with highly efficient photocathodic protection under visible-light illumination.

Study on the enhanced electron-hole separation capability of IrxZn1-xO/Ti electrodes with high photoelectrocatalysis efficiency

Making full use of low-energy photons and reducing photogenerated carriers' recombination rate have been considered important ways to raise photoelectrocatalysis (PEC) efficiency. In this study, Ir-doped ZnO PEC electrodes were prepared by thermal decomposition method, first principles calculations were used to study the effects of Ir content on the electronic structure and optical properties of Ir_xZn_1-xO coatings, the PEC degradation mechanism of the Ir_xZn_1-xO/Ti electrodes was also tentatively presented. The results indicated that with numbers of Zn atoms replaced by Ir atoms, impurity energy level appeared in ZnO band gap, which reduced the electron transition barriers and increased the number of photogenerated carriers. Besides, IrO₂ nanoparticles covered on ZnO nanorods surface, acting as highly efficient electron transfer channels and electrocatalytic active sites, could separate photogenerated electron-hole pairs and enhance PEC performance effectively. PEC performance of Ir_xZn_1-xO/Ti electrodes with different Ir contents under UV irradiation was evaluated by rhodamine B (RhB) removal rate. Compared with pure ZnO electrodes, Ir_xZn_1-xO/Ti ones exhibited much stronger degradation capacity. Specifically, Ir_0.09375Zn_0.90625O/Ti electrodes showed the highest degradation rate of 99.4 %, and a relatively high rate of 95.2 % after working 100 h continuously, indicating its excellent long-term stability.

Tuning wall thickness of TiO2 microtubes for an enhanced photocatalytic activity with thickness-dependent charge separation efficiency

TiO₂ microtubes with tunable wall thickness have been synthesized by a one-step electrospinning method linked with a calcination process. The wall thickness of TiO₂ microtubes can be easily tuned by altering the dosage of liquid paraffin. The influence of the thickness on the light-harvesting ability and separation efficiency of the photogenerated carriers was studied using ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, photoluminescence emission spectroscopy, and photocurrent density measurements. Results show that TiO₂ microtubes with an appropriate thickness exhibit enhanced light scattering effect, UV-vis light-harvesting ability, charge separation efficiency, and photocatalytic performance. The degradation rates of rhodamine B and 2,4-dinitrophenol by using TiO₂ microtubes synthesized at a dosage of 0.14 g/mL liquid paraffin are 99.9% within 60 min and 97.8% within 40 min, respectively, which are higher than most of the reported values. All these results suggest that our work provides an ideal strategy for adjusting the wall thickness of TiO₂ microtubes and new approach to enhance the photocatalytic performance of TiO₂.

Flexible Carbon-Fiber/Semimetal Bi Nanosheet Arrays as Separable and Recyclable Plasmonic Photocatalysts and Photoelectrocatalysts

In this work, we prepared flexible carbon-fiber/semimetal Bi nanosheet arrays from solvothermal-synthesized carbon-fiber/Bi₂O₂CO₃ nanosheet arrays via a reductive calcination process. The flexible carbon-fiber/semimetal Bi nanosheet arrays can function as photocatalysts and photoelectrocatalysts for 2,4-dinitorphenol oxidation. Compared with carbon-fiber/Bi₂O₂CO₃ nanosheet arrays, the newly designed flexible carbon-fiber/semimetal Bi nanosheet arrays show enhanced ultraviolet-visible (UV-vis) light absorption efficiency and photocurrent, photocatalytic, and photoelectrocatalytic activities. Photocatalytic analyses indicate that the surface plasmon resonance (SPR) of semimetal Bi occurs under solar-simulated light irradiation during the photocatalytic process. The carbon-fiber traps the hot electrons exerted from the SPR of semimetal Bi and creates holes in the semimetal Bi nanosheets, which boosts the photocatalytic activity of the carbon fiber through plasmonic sensitization. Both photocatalytic experiments and density functional theory (DFT) calculations indicate that the electrons transferred to the carbon fiber and the holes created in semimetal Bi contribute to the formation of •O₂^- and •OH, respectively. The synergistic effect between electrocatalysis and photocatalysis under the solar-simulated light results in almost complete degradation of 2,4-dinitorphenol during the photoelectrocatalytic process. This work realizes a non-noble-metal plasmonic catalyst and provides a new avenue for the commercialization of photocatalysis and photoelectrocatalysis using the separable and recyclable carbon-fiber/semimetal Bi nanosheet arrays in the environment-related field.

Copper doping and organic sensitization enhance photocatalytic activity of titanium dioxide: Efficient degradation of phenol and tetrabromobisphenol A

A novel photocatalyst (Cu-TiO₂@HQ) had been synthesized by combining Cu-doped TiO₂ nanoparticles with 8-Hydroxyquinoline (HQ) via hydrothermal method. The photocatalytic activities of Cu-TiO₂@HQ were investigated by using phenol and tetrabromobisphenol A (TBBPA) as target pollutants, respectively. The results indicated that the degradation efficiencies of phenol and TBBPA by Cu-TiO₂@HQ were 99.2% (in 30 min) and 99.4% (in 10 min) under visible light irradiation. Both of them were much better than that of pure TiO₂ (8.63% in 30 min) and Cu-TiO₂ (14.74% in 30 min). When phenol or TBBPA were degraded together with the reduction of Cr (VI), the reaction rate of each pollutant was significantly increased, and the cyclic stability of photocatalyst Cu-TiO₂@HQ was greatly improved. Based on the spectroscopic and photoelectric characteristic analysis we found that in the mixture of phenol-Cr (VI) or TBBPA-Cr (VI) both photo-generated electrons and holes can be consumed simultaneously, thus preventing their recombination. The possible degradation products of phenol and TBBPA including its degradation path way were also analyzed by high resolution liquid chromatography-mass spectrometry-mass spectrometry.