2D/2D CsPbBr3/BiOCl Heterojunction with an S-Scheme Charge Transfer for Boosting the Photocatalytic Conversion of CO2

DFT and experimental studies of the facet-dependent oxygen vacancies modulated WS2/BiOCl-OV S-scheme structure for enhanced photocatalytic removal of ciprofloxacin from wastewater

The present study explores visible light-assisted photodegradation of ciprofloxacin hydrochloride (CIP) antibiotic as a promising solution to water pollution. The focus is on transforming the optical and electronic properties of BiOCl through the generation of oxygen vacancies (OVs) and the exposure of (110) facets, forming a robust S-scheme heterojunction with WS2. The resultant OVs mediated composite with an optimal ratio of WS2 and BiOCl-OV (4-WS2/BiOCl-OV) demonstrated remarkable efficiency (94.3%) in the visible light-assisted photodegradation of CIP antibiotic within 1.5 h. The CIP degradation using 4-WS2/BiOCl-OV followed pseudo-first-order kinetics with the rate constant of 0.023 min-1, outperforming bare WS2, BiOCl, and BiOCl-OV by 8, 6, and 4 times, respectively. Density functional theory (DFT) analysis aligned well with experimental results, providing insights into the structural arrangement and bandgap analysis of the photocatalysts. Liquid chromatography-mass spectrometry (LC-MS) analysis utilized for identifying potentially degraded products while scavenging experiments and electron paramagnetic resonance (EPR) spin trapping analysis elucidated the S-scheme charge transfer mechanism. This research contributes to advancing the design of oxygen vacancy-mediated S-scheme systems in the realm of photocatalysis, with potential implications for addressing water pollution concerns.

Integrating bimetallic borides with g-C3N4 containing cyanamide defects for efficient photocatalytic nitrogen fixation

The sustainable generation of ammonia by photocatalytic nitrogen fixation under mild conditions is fascinating compared to conventional industrial processes. Nevertheless, owing to the low charge transfer efficiency, the insufficient light absorption capacity and limited active sites of the photocatalyst cause the difficult adsorption and activation of N2 molecules, thereby resulting in a low photocatalytic conversion efficiency. Herein, a novel bimetallic CoMoB nanosheets (CoMoB) co-catalyst modified carbon nitride with dual moiety defects (CN-TH3/3) Schottky junction photocatalyst is designed for photocatalytic nitrogen reduction reaction (NRR). The photocatalytic nitrogen reduction rate of the optimized CoMoB/CN-TH3/3 photocatalyst is 4.81 mM·g-1·h-1, which is 6.2 and 2.2 times higher than carbon nitride (CN) (0.78 mM·g-1·h-1) and CN-TH3/3 (2.21 mM·g-1·h-1), respectively. The excellent photocatalytic NRR performance is ascribed not only to the introduction of dual moiety defects (cyano and cyanamide groups) that extends the visible light absorption range and promotes exciton polarization dissociation, but also to the formation of interfacial electric field between CoMoB and CN-TH3/3, which effectively facilitates the interfacial charge transfer. Thus, the synergistic interaction between CN-TH3/3 and CoMoB further increases the electron numble of CoMoB active sites, which effectively strengthens the adsorption and activation of N2 and weakens the NN triple bond, thereby enhancing the photocatalytic NRR activity. This work highlights the introduced dual moiety defects and bimetallic CoMoB co-catalyst to synergistically enhance the photocatalytic nitrogen reduction performance.

Recent advances on bismuth oxyhalides for photocatalytic CO2 reduction

Photocatalytic conversion of CO2 into fuels such as CO, CH4, and CH3OH, is a promising approach for achieving carbon neutrality. Bismuth oxyhalides (BiOX, where X = Cl, Br, and I) are appropriate photocatalysts for this purpose due to the merits of visible-light-active, efficient charge separation, and easy-to-modify crystal structure and surface properties. For practical applications, multiple strategies have been proposed to develop high-efficiency BiOX-based photocatalysts. This review summarizes the development of different approaches to prepare BiOX-based photocatalysts for efficient CO2 reduction. In the review, the fundamentals of photocatalytic CO2 reduction are introduced. Then, several widely used modification methods for BiOX photocatalysts are systematacially discussed, including heterojunction construction, introducing oxygen vacancies (OVs), Bi-enrichment, heteroatom-doping, and morphology design. Finally, the challenges and prospects in the design of future BiOX-based photocatalysis for efficient CO2 reduction are examined.

In Situ Metal-Oxygen-Hydrogen Modified B-Tio2 @Co2 P-X S-Scheme Heterojunction Effectively Enhanced Charge Separation for Photo-assisted Uranium Reduction

Photo-assisted uranium reduction from uranium mine wastewater is expected to overcome the competition between impurity ions and U(VI) in the traditional process. Here, B-TiO2 @Co2 P-X S-scheme heterojunction with metal-oxygen-hydrogen (M-O-H) is developed insitu modification for photo-assisted U(VI) (hexavalent uranium) reduction. Relying on the DFT calculation and Hard-Soft-Acid-Base (HSAB) theory, the introduction of metal-oxygen-hydrogen (M-O-H, hard base) metallic bonds in the B-TiO2 @Co2 P-X is found to enhance the hydrophilicity and the capture capability for uranyl ion (hard acid). Accordingly, B-TiO2 @Co2 P-500 hybrid nanosheets exhibit excellent U(VI) reduction ability (>98%) in the presence of competing ions. By self-consistent energy band calculations and in-situ KPFM spectral analysis, the formation of the internal electric field between B-TiO2 and Co2 P at the heterojunction is proven, offering a strong driving force and atomic transportation highway for accelerating the S-scheme charge carriers directed migration and promoting the photocatalytic reduction of uranium. This work provides a valuable route to explore the functionally modified photocatalyst with high-efficiency photoelectron separation for U(VI) reduction.

Pillar-Layered Porous Metal-Organic Frameworks with Co2N2O8 Clusters and Tetragonal Ligands for CO2 Conversion

Converting CO2 to valuable chemicals and fuels is a viable method to establish a carbon-neutral energy cycle in the environment. Metal-organic frameworks (MOFs), characterized by dispersed active sites, high porosity, etc., have displayed a great application prospect in the electrochemical/chemical CO2 reduction reaction (CO2RR) process. Herein, we proposed a one-step production to establish a series of pillar-layered porous MOFs, [Co2(L)(bimb)]n (MOF 1) and [Co4(L)2(bidpe)2]n (MOF 2) [H4L = 5'-(4-carboxyphenyl)-(1,1':2',1″-terphenyl)-4,4',4″-tricarboxylic, bimb = 1,4-bis(imidazol-1-yl)-butane, bidpe = 4'-bis(imidazolyl) diphenyl ether], for preferential conversion of CO2 via ligand adjustment and increase of active sites' density. According to single-crystal X-ray diffraction studies, [Co2(L)(bimb)]n exhibits pillar-layered binuclear 3D frameworks with a 2,4,6-linked 3-nodes new topology structure, while [Co4(L)2(bidpe)2]n displays pillar-layered tetranuclear interspersed networks with a 4,6-linked 2-nodes fsc topology structure through a ligand adjustment strategy. Meanwhile, the pillar-layered structure of the MOFs with abundant active sites is conducive to mass diffusion and benefits the conversion of CO2. MOFs 1-2 exhibit good electrocatalytic activity for CO2RR in 0.5 M KHCO3 solution. Especially, the current density of MOF 2 generated at -0.90 V (vs. RHE) reaches -81.6 mA·cm-2, which is 3.1 times higher than that under an Ar atmosphere. In addition, MOFs 1-2 can be used as a heterogeneous catalyst for chemical conversion of CO2. The results are expected to provide inspiration for rational design to develop stable and high-efficiency MOF-based electrocatalysts for CO2RR.

Utilizing the Undesirable Oxidation of Lead-Free Hybrid Halide Perovskite Nanosheets for Solar-Driven Photocatalytic C(sp3)─H Activation: Unraveling the Serendipity

Hybrid halide perovskites (HHPs), whose every branch generates intrusiveness, have been utilized in solar cells from a broader perspective. However, the inclusiveness of employing HHP as a photocatalyst is in its initial stage. This study mainly focuses on the unexpected utilization of, so far, undesirable material vacancy-ordered MA2SnBr6 quantum dots synthesized from MASnBr3 nanosheets. Here, the quantum confinement grounded a large blue shift in ultraviolet (UV) and photoluminescence (PL) spectra with a Stokes shift of 420 meV, where the band gap increase is observed as size decreases in MA2SnBr6. Remarkably, MA2SnBr6 exhibits air and moisture stability, better charge transfer, and high oxidation potential compared to MASnBr3. The first-principles-based atomistic computations reveal the strain relaxation in the Sn-Br framework that structurally stabilizes the MA2SnBr6 lattice. Furthermore, the direct band gap and strongly localized valence band edge give rise to a new potential photocatalyst MA2SnBr6 for efficient solar-driven C(sp3)─H activation of cyclohexane and toluene under ambient conditions.

Improved visible light triggered photocatalytic activities of BiOCl photocatalysts via a synergistic effect of doping and heterojunction engineering

To manipulate the photocatalytic activities of BiOCl photocatalysts, doping and heterojunction engineering are simultaneously adopted. Herein, the photocatalysts Sm3+-doped BiOCl and BiOCl:Sm3+@yg-C3N4 were designed, in which their phase structure, morphology, optical properties and photocatalytic activities were systematically discussed. Excited at 408 nm, red emissions are seen from Sm3+-doped BiOCl microplates and their intensities were impacted by doping content, reaching the maximum value when the Sm3+ content was 1 mol% and the involved concentration mechanism was dominated by quadrupole-quadrupole interaction. Through analyzing the degradation of TC, the visible light triggered photocatalytic behaviors of the resultant compounds were studied. Compared with BiOCl microplates, an improved TC removal ability was seen in Sm3+-doped BiOCl microplates and the products with a Sm3+ content of 0.5 mol% show the best performance. Moreover, through constructing the heterojunction with g-C3N4, the TC removal capacity was further enhanced and the BiOCl:Sm3+@60%g-C3N4 exhibits the optimal photocatalytic activity, which was also much better than that of the commercial SnO2 and TiO2. Accordingly, the ˙O2-, h+ and ˙OH active species were proven to contribute to the involved visible light driven photocatalytic mechanism. Furthermore, the separation and recombination of photogenerated carries via the Z-scheme transfer process in the designed heterojunction composites, led to splendid photocatalytic properties. Additionally, it was verified that the TC solution treated with synthesized compounds was nontoxic toward plant growth. Our findings may propose an available route to regulate the photocatalytic performance of the visible light driven photocatalysts.

Synergistic Effects of the Ni3B Cocatalyst and N Vacancy on g-C3N4 for Effectively Enhanced Photocatalytic N2 Fixation

The photocatalytic fixation of N₂ is a promising technology for sustainable production of ammonia, while the unsatisfactory efficiency resulting from the low electron-transfer rate, narrow light absorption range, and limited active sites of the photocatalyst seriously hinder its application. Herein, we designed a noble metal-free Schottky junction photocatalyst constructed by g-C₃N₄ nanosheets with N vacancies (V_N-CN) and metallic Ni₃B nanoparticles (Ni₃B/V_N-CN) for N₂ reduction to ammonia. The ammonia yield rate over the optimized Ni₃B/V_N-CN is 7.68 mM g^-1 h^-1, which is 6.7 times higher than that of pristine CN (1.15 mM g^-1 h^-1). The superior photocatalytic N₂ fixation performance of Ni₃B/V_N-CN can be attributed not only to the formation of Schottky junctions between Ni₃B and V_N-CN, which facilitates the migration and separation of photogenerated electrons, but also to the incorporation of V_N into g-C₃N₄, which enhances visible light absorption and improves electrical conductivity. More importantly, Ni₃B nanoparticles can act as the cocatalyst, which provide more active sites for the adsorption and activation of N₂, thereby improving the N₂ reduction activity. This work provides an effective strategy of designing noble metal-free-based cocatalyst photocatalyst for sustainable and economic N₂ fixation.

Photoelectrochemical sensors based on paper and their emerging applications in point-of-care testing

Point-of-care testing (POCT) technology is urgently required owing to the prevalence of the Internet of Things and portable electronics. In light of the attractive properties of low background and high sensitivity caused by the complete separation of excitation source and detection signal, the paper-based photoelectrochemical (PEC) sensors, featured with fast in analysis, disposable and environmental-friendly have become one of the most promising strategies in POCT. Therefore, in this review, the latest advances and principal issues in the design and fabrication of portable paper-based PEC sensors for POCT are systematically discussed. Primarily, the flexible electronic devices that can be constructed by paper and the reasons why they can be used in PEC sensors are expounded. Afterwards, the photosensitive materials involved in paper-based PEC sensor and the signal amplification strategies are emphatically introduced. Subsequently, the application of paper-based PEC sensors in medical diagnosis, environmental monitoring and food safety are further discussed. Finally, the main opportunities and challenges of paper-based PEC sensing platforms for POCT are briefly summarized. It provides a distinct perspective for researchers to construct paper-based PEC sensors with portable and cost-effective, hoping to enlighten the fast development of POCT soon after, as well as benefit human society.

In Situ Growth of Lead-Free Cs2CuBr4 Perovskite Quantum Dots in KIT-6 Mesoporous Molecular Sieve for CO2 Adsorption, Activation, and Reduction

Metal halide perovskites (MHPs) are emerging as promising candidates for photocatalytic CO₂ conversion. However, their practical application is still restricted by the poor intrinsic stability and weak adsorption/activation toward CO₂ molecules. The rational design of MHPs-based heterostructures with high stability and abundant active sites is a potential solution to this obstacle. Herein, we report the in situ growth of lead-free Cs₂CuBr₄ perovskite quantum dots (PQDs) in KIT-6 mesoporous molecular sieve, obtaining remarkable photocatalytic CO₂ reduction activity and durable stability. The optimized Cs₂CuBr₄@KIT-6 heterostructure exhibits the photocatalytic CO and CH₄ evolution rates of 51.6 and 17.2 μmol g^-1 h^-1, respectively, far exceeding those of pristine Cs₂CuBr₄. On the basis of in situ diffuse reflectance infrared Fourier transform spectra and theoretical investigations, the detailed CO₂ photoreduction pathway is systematically revealed. This work provides a new route for the rational construction of perovskite-based heterostructures with strong CO₂ adsorption/activation and good stability for photocatalytic CO₂ reduction.

Construction of S-Scheme CuS/Bi5O7I Heterojunction for Boosted Photocatalytic Disinfection with Visible Light Exposure

In this paper, a novel S-scheme CuS/Bi5O7I heterojunction was successfully constructed using a two-step approach comprising the alkaline hydrothermal method and the adsorption–deposition method, and it consisted of Bi5O7I microrods with CuS particles covering the surface. The photocatalytic antibacterial effects on Escherichia coli (E. coli) were systematically examined with visible light exposure. The results suggested that the 3%-CuS/Bi5O7I composite showed the optimal antibacterial activity, completely inactivating E. coli (5 × 108 cfu/mL) in 180 min of irradiation. Moreover, the bacterial inactivation process was scientifically described. •O2− and h+ were the major active species for the inactivation of the bacteria. In the early stages, SOD and CAT initiated the protection system to avoid the oxidative destruction of the active species. Unfortunately, the antioxidant protection system was overwhelmed thereafter, which led to the destruction of the cell membrane, as evidenced by the microstructure changes in E. coli cells. Subsequently, the leakage of intracellular components including K+, proteins, and DNA resulted in the unavoidable death of E. coli. Due to the construction of the S-scheme heterojunction, the CuS/Bi5O7I composite displayed the boosted visible light harvesting, the high-efficiency separation of photogenerated electrons and holes, and a great redox capacity, contributing to an outstanding photocatalytic disinfection performance. This work offers a new opportunity for S-scheme Bi5O7I-based heterojunctions with potential application in water disinfection.

BiOCl Heterojunction photocatalyst: Construction, photocatalytic performance, and applications

BiOCl semiconductors have attracted extensive amounts of attention and have substantial potential in alleviating energy shortages, improving sterilization performance, and solving environmental issues. To improve the optical quantum efficiency of layered BiOCl, the lifetimes of photogenerated electron-hole pairs, and BiOCl reduction capacity. During the past decade, researchers have designed many effective methods to weaken the effects of these limitations, and heterojunction construction is regarded as one of the most promising strategies. In this paper, BiOCl heterojunction photocatalysts designed and synthesized by various research groups in recent years were reviewed, and their photocatalytic properties were tested. Among them, direct Z-scheme and S-scheme photocatalysts have high redox potentials and intense redox capabilities. Hence, they exhibit excellent photocatalytic activity. Furthermore, the applications of BiOCl heterojunctions for pollutant degradation, CO₂ reduction, water splitting, N₂ fixation, organic synthesis, and tumor ablation are also reviewed. Finally, we summarize research on the BiOCl heterojunctions and put forth new insights on overcoming their present limitations.

NiFe-Layered Double Hydroxides/Lead-free Cs2AgBiBr6 Perovskite 2D/2D Heterojunction for Photocatalytic CO2 Conversion

Designing of heterojunction photocatalysts with appropriate interfacial contact plays crucial roles in enhancing the interfacial charge transfer/separation. A two-dimensional (2D)/2D face-to-face heterojunction is an ideal option since this architecture with a large contact area can provide abundant reactive centers and promote the interfacial charge transfer/separation between layers. Herein, a novel 2D/2D heterojunction of NiFe-layered double hydroxides (NiFe-LDH)/Cs₂AgBiBr₆ (CABB) was fabricated by electrostatic self-assembly of NiFe-LDH and CABB nanosheets. This unique 2D/2D architecture endowed NiFe-LDH/CABB with a large contact area and a short charge transport distance, assuring remarkable interfacial charge transfer/separation rates. As a result, the 2D/2D NiFe-LDH/CABB heterojunction exhibited significant improvement in photocatalytic CO₂ reduction under visible light than the pristine counterparts. Based on density functional theory calculations and various characterizations, a step scheme charge-transfer mechanism was proposed. This investigation sheds light on the designing and manufacturing of highly efficient 2D/2D heterostructure photocatalysts for artificial photosynthesis.

Recent Progress in Halide Perovskite Nanocrystals for Photocatalytic Hydrogen Evolution

Due to its environmental cleanliness and high energy density, hydrogen has been deemed as a promising alternative to traditional fossil fuels. Photocatalytic water-splitting using semiconductor materials is a good prospect for hydrogen production in terms of renewable solar energy utilization. In recent years, halide perovskite nanocrystals (NCs) are emerging as a new class of fascinating nanomaterial for light harvesting and photocatalytic applications. This is due to their appealing optoelectronic properties, such as optimal band gaps, high absorption coefficient, high carrier mobility, long carrier diffusion length, etc. In this review, recent progress in halide perovskite NCs for photocatalytic hydrogen evolution is summarized. Emphasis is given to the current strategies that enhance the photocatalytic hydrogen production performance of halide perovskite NCs. Some scientific challenges and perspectives for halide perovskite photocatalysts are also proposed and discussed. It is anticipated that this review will provide valuable references for the future development of halide perovskite-based photocatalysts used in highly efficient hydrogen evolution.

Effect of Thermal Treatment of Symmetric TiO2 Nanotube Arrays in Argon on Photocatalytic CO2 Conversion

Symmetric titania nanotube arrays (TiO2 NTs) are a well-known photocatalyst with a large surface area and band edge potentials suitable for redox reactions. Thermal treatment of symmetrical arrays of TiO2 nanotubes in argon was used to change the carbon content of the samples. The influence of the carbon content in the structure of symmetrical TiO2 NTs on their photoelectrochemical properties and photocatalytic activity in the conversion of CO2 into organic fuel precursors has been studied. The structure, chemical, and phase composition of obtained samples were studied by X-ray analysis, Raman spectroscopy, and SEM with energy dispersive analysis. It is established that carbon-related defects in the samples accumulate electrons on the surface required for the CO2 conversion reaction. It has been shown for the first time that varying the carbon content in symmetric TiO2 NTs arrays by annealing at different temperatures in argon makes it possible to control the yield of methane and methanol in CO2 conversion. It is revealed that too high a concentration of carbon dangling bonds promotes the growth of CO2 conversion efficiency but causes instability in this process. The obtained results show a high promise of symmetric carbon-doped TiO2 NTs arrays for the photocatalytic conversion of CO2.

Recent advances in bismuth oxyhalides photocatalysts and their applications

Bismuth oxyhalides photocatalysts exhibit great potential to solve the energy and environmental issues under visible light due to their unique physicochemical and optical properties. However, the photocatalytic activity of pristine bismuth oxyhalides remains unsatisfactory because of their inherent drawbacks. Up to now, many strategies have been used to improve the photocatalytic performance. In this review, the basic mechanism, unique properties and structure of bismuth oxyhalides photocatalysts have been introduced, and the common techniques of synthesis, modification, and main applications have been discussed. Finally, new insights are proposed to meet the future challenges and development of the photocatalysts, which can provide better knowledge for the advancement of the related research areas.

Ni3B as p-Block Element-Modulated Cocatalyst for Efficient Photocatalytic CO2 Reduction

Due to the multiple electron and proton transfer processes involved, the photogenerated charges are easily recombined during the photocatalytic reduction of CO₂, making the generation of the eight-electron product CH₄ kinetically more difficult. Herein, Ni₃B nanoparticles modulated by p-block element were combined with TiO₂ nanosheets to construct a novel Schottky junction photocatalyst (Ni₃B/TiO₂) for the selective photocatalytic conversion of CO₂ to CH₄. The formed Ni₃B/TiO₂ photocatalyst with Schottky junction ensures a transfer pathway of photogenerated electrons from TiO₂ to Ni₃B, which facilitates the accumulation of electrons on the surface of Ni₃B and subsequently improves the activity of photocatalytic CO₂ reduction to CH₄. The optimized Ni₃B/TiO₂ Schottky junction shows an improved CH₄ yield of 30.03 μmol g^-1 h^-1, which was much higher than those of TiO₂ (1.62 μmol g^-1 h^-1), NiO/TiO₂ (2.44 μmol g^-1 h^-1), and Ni/TiO₂ (4.3 μmol g^-1 h^-1). This work demonstrated that the introduction of p-block elements can alleviate the scaling relationship effect of pure metal cocatalysts to a certain extent, and the modified Ni₃B can be used as a promising new cocatalyst to effectively improve the selective photocatalytic of CO₂ to CH₄.

Boosting Interfacial Charge Transfer with a Giant Internal Electric Field in a TiO2 Hollow-Sphere-Based S-Scheme Heterojunction for Efficient CO2 Photoreduction

The construction of an S-scheme charge transfer pathway is considered to be a powerful way to inhibit charge recombination and maintain photogenerated carriers with high redox capacity to meet the kinetic requirements of the carbon dioxide (CO₂) photoreduction reaction. For an S-scheme heterojunction, an internal electric field (IEF) is regarded as the main driving force for accelerating the interfacial spatial transfer of photogenerated charges. Herein, we designed a TiO₂ hollow-sphere (TH)-based S-scheme heterojunction for efficient CO₂ photoreduction, in which WO₃ nanoparticles (WP) were applied as an oxidation semiconductor to form an intimate interfacial contact with the TH. The S-scheme charge transfer mode driven by a strong IEF for the TH/WP composite was confirmed by in situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. As a result, abundant photogenerated electrons with strong reducing ability would take part in the CO₂ reduction reaction. The combination of surface photovoltage spectra and transient photocurrent experiments disclosed that the IEF intensity and charge separation efficiency of the fabricated TH/WP composite were nearly 16.80- and 1.42-fold higher, respectively, than those of the pure TH. Furthermore, sufficient active sites provided by the hollow-sphere structure also enhanced the kinetics of the catalytic reaction. Consequently, the optimized TH/WP composite showed a peak level of CO production of 14.20 μmol g^-1 in 3 h without the addition of any sacrificial agent. This work provides insights into the kinetic studies of the S-scheme charge transfer pathway for realizing high-performance CO₂ photoreduction.