Design of Heterostructured Hollow Photocatalysts for Solar-to-Chemical Energy Conversion

Multi-channel charge transfer of hierarchical TiO2 nanosheets encapsulated MIL-125(Ti) hollow nanodisks sensitized by ZnSe for efficient CO2 photoreduction

Metal-organic frameworks-based hybrids with desirable components, structures, and properties have been proven to be promising functional materials for photocatalysis and energy conversion applications. Herein, we proposed and prepared ZnSe sensitized hierarchical TiO₂ nanosheets encapsulated MIL-125(Ti) hollow nanodisks with sandwich-like structure (MIL-125(Ti)@TiO₂\ZnSe HNDs) through a successive solvothermal and selenylation reaction route using the as-prepared MIL-125(Ti) nanodisks as precursor. In the ternary MIL-125(Ti)@TiO₂\ZnSe HNDs hybrid, TiO₂ nanosheets were transformed from MIL-125(Ti) and in situ grown on both sides of the MIL-125(Ti) shell, forming sandwich-like hollow nanodisks, and the ratio of MIL-125(Ti)/TiO₂ can be tuned by changing the solvothermal time. The ternary hybrids possess the advantages of enhanced incident light utilization and abundant accessible active sites originating from bimodal pore-size distribution and hollow sandwich-like heterostructure, which can effectively promote CO₂ photoreduction reaction. Especially, the formed multi-channel charge transfer routes in the ternary heterojunctions contribute to the charge transfer/separation and extend the lifespan of charge-separated state, thus boosting CO₂ photoreduction performance. The CO (513.1 μmol g^-1h^-1) and CH₄ (45.1 μmol g^-1h^-1) evolution rates over the optimized ternary hybrid were greatly enhanced compared with the single-component and binary hybrid photocatalysts.

In situ growth of WO3/BiVO4 nanoflowers onto cellulose fibers to construct photoelectrochemical/colorimetric lab-on-paper devices for the ultrasensitive detection of AFP

In this work, novel dual-mode lab-on-paper devices based on in situ grown WO₃/BiVO₄ heterojunctions onto cellulose fibers, as signal amplification probes, were successfully fabricated by the integration of photoelectrochemical (PEC)/colorimetric analysis technologies into a paper sensing platform for the ultrasensitive detection of alpha-fetoprotein (AFP). Specifically, to achieve an impressive PEC performance of the lab-on-paper device, the WO₃/BiVO₄ heterojunction was in situ grown onto the surface of cellulose fibers assisted with Au nanoparticle (Au NP) functionalization for enhancing the conductivity of the working zone of the device. With the target concentration increased, more immune conjugates could be captured by the proposed paper photoelectrode, which could lead to a quantitative decrease in the photocurrent intensity, eventually realizing the accurate PEC signal readout. To meet the requirement of end-user application, a colorimetric signal readout system was designed for the lab-on-paper device based on the color reaction of 3,3'5,5'-tetramethylbenzidine (TMB) oxidized by WO₃/BiVO₄ nanoflowers in the presence of H₂O₂. Noticeably, it is the first time that the WO₃/BiVO₄ heterojunction is in situ grown onto cellulose fibers, which enhances the sensitivity in view of both their PEC activity and catalytic ability. By controlling the conversion process of hydrophobicity and hydrophilicity on the lab-on-paper device combined with diverse origami methods, the dual-mode PEC/colorimetric signal output for the ultrasensitive AFP detection was realized. Under optimal conditions, the proposed dual-mode lab-on-paper device could enable the sensitive PEC/colorimetric diagnosis of AFP in the linear range of 0.09-100 ng mL^-1 and 5-100 ng mL^-1 with the limit of detection of 0.03 and 1.47 ng mL^-1, respectively.

Design of MOF-Derived NiO-Carbon Nanohybrids Photocathodes Sensitized with Quantum Dots for Solar Hydrogen Production

Nickel oxide (NiO) is a promising p-type material for a wide range of optoelectronic devices, as well as photocathode for photoelectrochemical (PEC) water splitting. However, traditional NiO photoelectrodes exhibit a wide bandgap (3.6 eV), intrinsic poor electrical conductivity, and low surface area, leading to low PEC systems performance. Herein, the authors explore a Ni-based metal-organic framework (MOF) template method to obtain hierarchical hollow spheres of carbon/NiO nanostructure by successive carbonization and oxidation treatments. After sensitization with core and core-shell quantum dots (QDs), the optimized NiO-photocathode exhibits a maximum current density of -93.6 µA cm^-2 at 0 V versus RHE (reversible hydrogen electrode) in neutral pH (6.8) and -285 µA cm^-2 at -0.4 V versus RHE. Compared to pure NiO and single-core CdSe QDs, a 2.2-fold increase in photocurrent can be obtained. The improvement in the performance of this hybrid is not only due to the high surface area for loading QDs and light scattering, but also to the presence of a highly conductive carbon matrix that promotes fast charge transfer. The proposed MOFs-based NiO/carbon photocathode sensitized with QDs can be an effective strategy to improve the efficiency of metal oxide-based PEC systems for hydrogen generation.

Metal-Organic Framework-Derived Tubular In2O3-C/CdIn2S4 Heterojunction for Efficient Solar-Driven CO2 Conversion

Realizing high-efficiency solar-driven CO₂ reduction to chemicals and fuels requires high-performance photocatalysts with high utilization efficiency of solar light, efficient charge separation and transfer, and robust adsorption capacity for CO₂. In this work, a tubular In₂O₃-C/CdIn₂S₄ (IOC/CIS) ternary heterojunction with an intimate interfacial contact was fabricated by pyrolysis of In-MIL-68 and subsequent solvothermal synthesis of CdIn₂S₄. The construction of a heterojunction promotes the separation and transfer efficiency of photogenerated carriers. The introduction of carbon not only accelerates the interfacial charge migration but also enhances light absorption and CO₂ adsorption. The resulting 5IOC/CIS sample presents a remarkably improved photocatalytic CO₂ reduction activity with a CO generation rate of 2432 μmol g^-1 h^-1, much higher than that of the In₂O₃/CdIn₂S₄ (IO/CIS) heterojunction (1906 μmol g^-1 h^-1). Furthermore, the type II charge transfer mechanism of the heterojunction was confirmed by the electron paramagnetic resonance characterization. This work provides new insight into the design and preparation of a highly efficient hollow heterojunction for photocatalytic applications.

Steering the Pathway of Plasmon-Enhanced Photoelectrochemical CO2 Reduction by Bridging Si and Au Nanoparticles through a TiO2 Interlayer

Photoelectrochemical (PEC) conversion of CO₂ in an aqueous medium into high-energy fuels is a creative strategy for storing solar energy and closing the anthropogenic carbon cycle. However, the rational design of catalytic architectures to selectively and efficiently produce a target product such as CO has remained a grand challenge. Herein, an efficient and selective Si photocathode for CO production is reported by utilizing a TiO₂ interlayer to bridge the Au nanoparticles and n⁺ p-Si. The TiO₂ interlayer can not only effectively protect and passivate Si surface, but can also exhibit outstanding synergies with Au nanoparticles to greatly promote CO₂ reduction kinetics for CO production through stabilizing the key reaction intermediates. Specifically, the TiO₂ layer and Au nanoparticles work concertedly to enhance the separation of localized surface plasmon resonance generated hot carriers, contributing to the improved activity and selectivity for CO production by utilizing the hot electrons generated in Au nanoparticles during PEC CO₂ reduction. The optimized Au/TiO₂ /n⁺ p-Si photocathode exhibits a Faradaic efficiency of 86% and a partial current density of -5.52 mA cm^-2 at -0.8 V_RHE for CO production, which represent state-of-the-art performance in this field. Such a plasmon-enhanced strategy may pave the way for the development of high-performance PEC photocathodes for energy-efficient CO₂ utilization.

Fabrication of 2H/3C-SiC heterophase junction nanocages for enhancing photocatalytic CO2 reduction

The morphology and structure of photocatalyst play an important role in photocatalytic activity. SiC semiconductor is considered as a promising material for the photocatalytic CO₂ reduction due to its negative conduction band position. Herein, SiC nanocages is creatively synthesized by simple low-temperature molten-salt-mediated magnesiothermic reduction method with using SiO₂ as template. The morphology and phase composition of SiC nanocages can be controlled by magnesium dosage and reaction temperature. The 2H and 3C crystal phase in SiC nanocage can form heterophase junctions uniformly to effectively accelerate the photogenerated electron transfer, and plays a key role in improving the photocatalytic activity of 2H/3C-SiC samples. The optimal SiC nanocage sample possesses a CO generation rate of 4.68 μmol g^-1h^-1 for photocatalytic CO₂ reduction, which is 3.25 times higher than that of commercial SiC.

Hollow multi-shelled Co3O4 as nanoreactors to activate peroxymonosulfate for highly effective degradation of Carbamazepine: A novel strategy to reduce nano-catalyst agglomeration

Reducing the agglomeration of nano-catalysts to retain the active catalytic sites is crucial for the advanced oxidation processes (AOPs) of peroxymonosulfate activation in wastewater treatments. Herein, Co₃O₄ hollow multi-shelled structures (HoMSs) were successfully prepared as the nanoreactors to reduce the agglomeration of nano-catalysts in catalytic reaction. Compared with single-shelled and double-shelled Co₃O₄ HoMSs, triple-shelled Co₃O₄ HoMSs (TS-Co₃O₄) exhibited best catalytic performance and the carbamazepine (5 mg L^-1) degradation reached 100% within 30 min. The hollow multi-shelled structures showed a significant role in reducing the agglomeration of catalysts. The value of hydrodynamic diameter/true particle size of TS-Co₃O₄ was 1.58, which meant TS-Co₃O₄ could be regarded as a single dispersion or two together in aqueous solution. The shells of TS-Co₃O₄ supported each other and outer shells could protect the inner ones, hence the stability increased. Besides, the hollow cavity between shells reduced the mass diffusion resistance and increased the contact of reactants with active sites. Mechanism studies showed sulfate radicals (SO₄^•-) played a leading role in the degradation of carbamazepine. This work provided an effective way to reduce the agglomeration and retain the active sites of cobalt-based catalysts in AOPs, so as to balance the conflict between the reactivity and stability of nano-catalysts.

Molecular Design of Covalent Triazine Frameworks with Anisotropic Charge Migration for Photocatalytic Hydrogen Production

Covalent triazine frameworks (CTFs) represent promising polymeric photocatalysts for photocatalytic hydrogen production with visible light. However, the separation and transfer of charges in CTFs are isotropic because of the uniform distribution of donor-acceptor motifs in the skeleton. Herein, to achieve the anisotropic charge carrier separation and migration, thiophene (Th) or benzothiadiazole (BT) unit is selected as the dopant to modify the molecular structure of CTF-based photocatalysts. Both theoretical and experimental studies reveal that the incorporation of Th or BT units induces the anisotropic charge carrier separation and migration at the interface of CTFs. The optimized polymer manifests a much enhanced photocatalytic activity for photocatalytic hydrogen production with visible light, and thus this study provides a useful tool to design conjugated polymer photocatalysts at the molecular level for solar energy conversion.

Bacteria-Triggered Solar Hydrogen Production via Platinum(II)-Tethered Chalcogenoviologens

Multifunctional solar energy conversion offers a feasible strategy to solve energy, environmental and water crises. Herein, a series of platinum(II)-tethered chalcogenoviologens (PtL⁺ -EV²⁺ , E=S, Se, Te) is reported, which integrate the functions of photosensitizer, electron mediator and catalyst. PtL⁺ -EV²⁺ (particularly for PtL⁺ -SeV²⁺ )-based one-component solar H₂ production could be triggered not only by EDTA, but also by facultative anaerobic and aerobic bacteria relying on a simplified mechanism, along with efficient antibacterial activities. In addition, by using real pool water, PtL⁺ -SeV²⁺ achieved multiple functions, including H₂ production, antibacterial action and acid removal, which supplied a new strategy to solve various problems in real life via a single system.

Improvement in Structure and Visible Light Catalytic Performance of g-C3N4 Fabricated at a Higher Temperature

A highly-efficient graphitic carbon nitride (g-C3N4) photocatalyst for visible light photodegradation of rhodamine B (RhB) and methyl orange (MO) simulating dyeing wastewater was synthesized by the thermal polycondensation of melamine. The photocatalysts were characterized by TG-DTG-DSC, XRD, EA, XPS, FT-IR, SEM, TEM, BET, PL and UV-vis DRS. The results showed that the photocatalytic performance of g-C3N4 at a higher calcination temperature was significantly enhanced, and its photocatalytic activities for the photodegradation of RhB and MO were remarkably improved by 64.91% and 41.83%, respectively, which was mainly attributed to the satisfactory crystallinity, stable graphene-like structure, large surface area, and excellent optical properties. It was found that •O2− radicals and •OH radicals were the main active species for the photodegradation process by the free radicals trapping experiments and ESR analysis. The photodegradation mechanism of g-C3N4 was proposed predicated using the characterization results.

In-Situ Generated CsPbBr3 Nanocrystals on O-Defective WO3 for Photocatalytic CO2 Reduction

Metal halide perovskite (MHP) nanocrystals (NCs) have shown promising application in photocatalytic CO₂ reduction, but their activities are still largely restrained by severe charge recombination and narrow solar spectrum response. Assembly of heterojunctions can be beneficial to the charge separation in MHPs while the assembly process usually brings native interfacial defects, impeding efficient charge separation between two materials. Herein, an in-situ generation strategy was developed to prepare CsPbBr₃ /WO₃ heterojunction, using WO₃ nanosheets (NSs) as growing substrate for the growth of CsPbBr₃ NCs. The developed CsPbBr₃ /WO₃ heterojunction exhibited a high-quality interface, greatly facilitating charge transfer between two semiconductors. The hybrid photocatalyst displayed an excellent activity toward CO₂ reduction, which was about 7-fold higher than pristine CsPbBr₃ NCs and 3.5-fold higher than their assembled counterparts. The experimental results and theoretical simulations revealed that a Z-scheme mechanism with a favorable internal electric field was responsible for the good performance of CsPbBr₃ /WO₃ heterojunction. By using O-defective WO₃ NSs as a near-infrared (NIR) light absorber, the CsPbBr₃ /WO₃ heterojunction could harvest NIR light and showed an impressive activity toward CO₂ reduction. This work demonstrates a new strategy to design MHP-based heterojunctions by synergistically considering the interface quality, charge transfer mode, interfacial electric field, and light response range between two semiconductors.

Hierarchical CuS@ZnIn2S4 Hollow Double-Shelled p-n Heterojunction Octahedra Decorated with Fullerene C60 for Remarkable Selectivity and Activity of CO2 Photoreduction into CH4

In this work, a hollow double-shelled architecture, based on n-type ZnIn₂S₄ nanosheet-coated p-type CuS hollow octahedra (CuS@ZnIn₂S₄ HDSOs), is designed and fabricated as a p-n heterojunction photocatalyst for selective CO₂ photoreduction into CH₄. The resulting hybrids provide rich active sites and effective charge migration/separation to drive CO₂ photoreduction, and meanwhile, CO detachment is delayed to increase the possibility of eight-electron reactions for CH₄ production. As expected, the optimized CuS@ZnIn₂S₄ HDSOs manifest a CH₄ yield of 28.0 μmol g^-1 h^-1 and a boosted CH₄ selectivity up to 94.5%. The decorated C₆₀ both possesses high electron affinity and improves catalyst stability and CO₂ adsorption ability. Thus, the C₆₀-decorated CuS@ZnIn₂S₄ HDSOs exhibit the highest CH₄ evolution rate of 43.6 μmol g^-1 h^-1 and 96.5% selectivity. This work provides a rational strategy for designing and fabricating efficient heteroarchitectures for CO₂ photoreduction.

Rational construction of Ag3PO4/WO3 step-scheme heterojunction for enhanced solar-driven photocatalytic performance of O2 evolution and pollutant degradation

Heterojunction engineering has been regarded as a promising strategy to sufficiently utilizing photogenerated charge carriers, thus benefiting the improvement of photocatalytic performance. Herein, Ag₃PO₄/WO₃ S-scheme heterojunction was synthesized via a simple deposition-precipitation process, and its photocatalytic activity was evaluated by monitoring water splitting and pollutant degradation under visible light. As a result, Ag₃PO₄/WO₃ with optimized ratio photocatalyst showed enhanced photocatalytic activity in oxygen production (306.6 μmol·L^-1·h^-1) relative to pure Ag₃PO₄ (204.4 μmol·L^-1·h^-1). Additionally, it also exhibits rapid toxicity elimination efficiency over hexavalent chromium ions (Cr⁶⁺) and ciprofloxacin (CIP) with degrading rate of 72% and 83% within 30 min, respectively. According to a series characterization, a possible S-scheme photocatalytic mechanism of Ag₃PO₄/WO₃ was demonstrated in detail, which endowed the heterojunction with strong redox abilities to provide powerful diving force towards the photocatalytic reaction. This work presents an innovative perspective to construct Ag₃PO₄-based S-scheme heterojunctions for boosting photocatalytic performance for various applications.

Recent Advances in Porous Materials for Photocatalytic CO2 Reduction

Photocatalytic CO₂ reduction into solar fuels is a promising technology for addressing energy and CO₂ emission issues. Because of the superior properties in CO₂ adsorption and activation, molecular diffusion, light absorption, and charge separation and transfer, porous materials have been developed into a multifunctional platform for photocatalytic CO₂ reduction. In this Perspective, we first discuss the emerging trends of CO₂ reduction in major inorganic porous materials-based photocatalysts, such as mesoporous materials, macroporous materials, hollow materials, hierarchically porous materials, and zeolites. Prospects and challenges in the development of porous materials-based photocatalysts are then outlined. Finally, we envision feasible solutions for the deployment of porous materials to enhance photocatalytic CO₂ reduction performance.

Synergistically Modulating Geometry and Electronic Structures of a Chalcogenide Photocatalyst via an Ion-Exchange Strategy

Maneuvering the architecture and composition of semiconductors is essential to optimizing their performance in photocatalytic solar-to-fuel conversion. Here, we show that ion exchange, having a disparate mechanism with direct nucleation and growth of semiconductor crystals, can provide a new platform for rational control over the geometry and electronic structures of chalcogenide semiconductor photocatalysts. As a demonstration, the ZnSe nanocubes possessing a hollowed architecture and doped with a controllable amount of Ag⁺ ions are accessed via sequential ion exchange. The kinetics of the exchange reaction offers a knob for regulating the electronic structures of the Ag-doped ZnSe hollow cubes and, hence, their functions in light harvesting and photogenerated charge separation. Such synergistically geometric and optoelectronic modulation of ZnSe brings an order of magnitude enhancement in photocatalytic H₂ evolution activity relative to commercial ZnSe powders. Our study corroborates that ion exchange may open up new horizons for judicious fabrication and engineering of semiconductor-based photocatalyst materials.

Porous direct Z-scheme heterostructures of S-deficient CoS/CdS hexagonal nanoplates for robust photocatalytic H2 generation

Unique porous S-deficient CoS/CdS hexagonal nanoplates exhibited an outstanding photocatalytic capability for H2 production, due to excellent visible-light response, efficient Z-scheme charge separation, and abundant H2-evolving active sites.

Phase Segregation via Etching-Induced Cation Migration in CoSx-ZnS Nanoarchitectures for Solar Hydrogen Evolution

Low charge carrier mobility limits the development of highly efficient semiconductor-based photocatalysis. Heterointerface engineering is a promising approach to spatially separate the photoexcited charge carriers and thus enhance photocatalytic activity....

Aqueous broadband photopolymerization on microreactor arrays: from high throughput polymerization to fabricating artificial cells

Microreactor arrays combining ZnO and polyaniline are fabricated onto the bottom of multi-well plates to catalyze broadband sunlight-driven open-to-air polymerization in aqueous media.

SnS2 with Flower-like Structure for Efficient CO2 Photoreduction under Visible-Light Irradiation

Photocatalytic CO₂ reduction using solar energy is a promising way to obtain renewable-energy sources for replacing fossil fuels. Through a hydrothermal process, we successfully designed and synthesized three-dimensional (3D) flower-like structured SnS₂ with a sheet-like structured quasi-hexagon as the building block. The 3D hierarchical structure is conducive to light capture and absorption, the sheet structure can shorten the transmission path and promote separation of the carriers, and the self-supporting effect can effectively prevent catalyst agglomeration during the catalytic reaction. Therefore, when used in photocatalytic CO₂ reduction, SnS₂ with a flower-like structure showed excellent photocatalytic performance compared with SnS₂ nanoparticles (NPs) under visible-light irradiation with a gas-solid reaction system.

Recent Advances in MnOx/CeO2-Based Ternary Composites for Selective Catalytic Reduction of NOx by NH3: A Review

Recently, manganese oxides (MnOx)/cerium(IV) oxide (CeO2) composites have attracted widespread attention for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia (NH3), which exhibit outstanding catalytic performance owing to unique features, such as a large oxygen storage capacity, excellent low-temperature activity, and strong mechanical strength. The intimate contact between the components can effectively accelerate the charge transfer to enhance the electron–hole separation efficiency. Nevertheless, MnOx/CeO2 still reveals some deficiencies in the practical application process because of poor thermal stability, and a low reduction efficiency. Constructing MnOx/CeO2 with other semiconductors is the most effective strategy to further improve catalytic performance. In this article, we discuss progress in the field of MnOx/CeO2-based ternary composites with an emphasis on the SCR of NOx by NH3. Recent progress in their fabrication and application, including suitable examples from the relevant literature, are analyzed and summarized. In addition, the interaction mechanisms between MnOx/CeO2 catalysts and NOx pollutants are comprehensively dissected. Finally, the review provides basic insights into prospects and challenges for the advancement of MnOx/CeO2-based ternary catalysts.

Porous Ga2 O3 Nanotubes Derived from Urease-Mediated Interfacially-Grown NH4 Ga(OH)2 CO3 for High-Efficient Hydrogen Evolution

The authors proposed a novel template-free strategy, urease-mediated interfacial growth of NH₄ Ga(OH)₂ CO₃ nanotubes at 20-50 °C, to fabricate the porous Ga₂ O₃ nanotubes. The subtlety of the proposed strategy is all the products from urea enzymolysis are utilized in formation of NH₄ Ga(OH)₂ CO₃ precipitates, and the key for interfacial growth of NH₄ Ga(OH)₂ CO₃ nanotubes is the dynamic match between the rate of CO₂ bubble fusion and NH₄ Ga(OH)₂ CO₃ precipitation. The proposed strategy works well for the doped porous Ga₂ O₃ nanotubes. As a proof-of-concept, the porous β-Ga₂ O₃ and β-Ga₂ O₃ :Cr_0.001 nanotubes are used as photocatalysts or co-catalysts with Pt, for H₂ evolution from water splitting. The H₂ evolution rate of porous β-Ga₂ O₃ nanotubes reach 39.3 mmol g^-1 h^-1 with solar-to-hydrogen (STH) conversion efficiency of 2.11% (Hg lamp) or 498 µmol g^-1 h^-1 with STH of 0.03% (Xe lamp) respectively, both about 3 times of β-Ga₂ O₃ nanoparticles synthesized at pH 9.0 without urease. The Cr-doping enhances the in-the-dark H₂ evolution rate pre-lighted by Hg lamp, and Pt co-catalysis further elevates the H₂ evolution rate, for instance, the H₂ evolution rate of Pt-loaded β-Ga₂ O₃ :Cr_0.001 nanotubes reaches 54.7 mmol g^-1 h^-1 with STH of 2.94% under continuous lighting of Hg lamp and 1062 µmol g^-1 h^-1 in-the-dark.

Versatile Synthesis of Hollow Metal Sulfides via Reverse Cation Exchange Reactions for Photocatalytic CO2 Reduction

Herein, we explore a general Cu_2-x S nanocube template-assisted and reverse cation exchange-mediated growth strategy for fabricating hollow multinary metal sulfide. Unlike the traditional cation exchange method controlled by the metal sulfide constant, the introduction of tri-n-butylphosphine (TBP) can reverse cation exchange to give a series of hollow metal sulfides. A variety of hollow multinary metal sulfide cubic nanostructures has been demonstrated while preserving anisotropic shapes to the as-synthesized templates, including binary compounds (CdS, ZnS, Ag₂ S, PbS, SnS), ternary compound (CuInS₂ , Zn_x Cd_1-x S), and quaternary compound (single-atom platinum anchored Zn_x Cd_1-x S; Zn_x Cd_1-x S-Pt₁ ). Experimental and density functional theory (DFT) calculations show that the hollow metal sulfide semiconductors obtained could significantly improve the separation and migration of photogenerated electron-hole pairs. Owing to the efficient charge transfer, the Zn_x Cd_1-x S-Pt₁ exhibited outstanding photocatalytic performance of CO₂ to CO, with the highest CO generation rate of 75.31 μmol h^-1 .

Progress on photocatalytic semiconductor hybrids for bacterial inactivation

Due to its use of green and renewable energy and negligible bacterial resistance, photocatalytic bacterial inactivation is to be considered a promising sterilization process. Herein, we explore the relevant mechanisms of the photoinduced process on the active sites of semiconductors with an emphasis on the active sites of semiconductors, the photoexcited electron transfer, ROS-induced toxicity and interactions between semiconductors and bacteria. Pristine semiconductors such as metal oxides (TiO₂ and ZnO) have been widely reported; however, they suffer some drawbacks such as narrow optical response and high photogenerated carrier recombination. Herein, some typical modification strategies will be discussed including noble metal doping, ion doping, hybrid heterojunctions and dye sensitization. Besides, the biosafety and biocompatibility issues of semiconductor materials are also considered for the evaluation of their potential for further biomedical applications. Furthermore, 2D materials have become promising candidates in recent years due to their wide optical response to NIR light, superior antibacterial activity and favorable biocompatibility. Besides, the current research limitations and challenges are illustrated to introduce the appealing directions and design considerations for the future development of photocatalytic semiconductors for antibacterial applications.

In situ Irradiated XPS Investigation on S-Scheme TiO2 @ZnIn2 S4 Photocatalyst for Efficient Photocatalytic CO2 Reduction

Reasonable design of efficient hierarchical photocatalysts has gained significant attention. Herein, a step-scheme (S-scheme) core-shell TiO₂ @ZnIn₂ S₄ heterojunction is designed for photocatalytic CO₂ reduction. The optimized sample exhibits much higher CO₂ photoreduction conversion rates (the sum yield of CO, CH₃ OH, and CH₄ ) than the blank control, i.e., ZnIn₂ S₄ and TiO₂ . The improved photocatalytic performance can be attributed to the inhibited recombination of photogenerated charge carriers induced by S-scheme heterojunction. The improvement is also attributed to the large specific surface areas and abundant active sites. Meanwhile, S-scheme photogenerated charge transfer mechanism is testified by in situ irradiated X-ray photoelectron spectroscopy, work function calculation, and electron paramagnetic resonance measurements. This work provides an effective strategy for designing highly efficient heterojunction photocatalysts for conversion of solar fuels.

Enhanced Photocatalytic Antibacterial Properties of TiO2 Nanospheres with Rutile/Anatase Heterophase Junctions and the Archival Paper Protection Application

TiO2 has been generally studied for photocatalytic sterilization, but its antibacterial activities are limited. Herein, TiO2 nanospheres with rutile/anatase heterophase junctions are prepared by a wet chemical/annealing method. The large BET surface area and pore size are beneficial for the absorption of bacteria. The rutile/anatase heterojunctions narrow the bandgap, which enhances light absorption. The rutile/anatase heterojunctions also efficiently promote the photogenerated carriers' separation, finally producing a high yield of radical oxygen species, such as •O2- and •OH, to sterilize bacteria. As a consequence, the obtained TiO2 nanospheres with rutile/anatase heterojunctions present an improved antibacterial performance against E. coli (98%) within 3 h of simulated solar light irradiation, exceeding that of TiO2 nanospheres without annealing (amorphous) and TiO2 nanospheres annealing at 350 and 550 °C (pure anatase). Furthermore, we design a photocatalytic antibacterial spray to protect the file paper. Our study reveals that the TiO2 nanospheres with rutile/anatase heterojunctions are a potential candidate for maintaining the durability of paper in the process of archival protection.

Hierarchical Double-Shelled CoP Nanocages for Efficient Visible-Light-Driven CO2 Reduction

Visible-light-driven photocatalytic CO₂ reduction is considered an appealing strategy to mitigate the energy crisis and environmental issues, whereas the reactivity is limited due to the difficulties in activation of inert CO₂ molecule and efficient transportation of photoinduced carriers. Herein, we report the design of novel Fe doped CoP hierarchical double-shelled nanocages (Fe-CoP HDSNC) via a MOF-templated approach for highly efficient visible-light-driven CO₂ reduction. The unique hierarchical double-shelled hollow architectures can greatly shorten the charge transfer distances and also expose abundant reactive sites. Moreover, Fe atoms doping is able to reduce the CO₂ activation energy barrier through stabilizing the *COOH intermediates and promote the CO desorption by destabilizing the CO* adduct. As expected, the Fe-CoP HDSNC achieves an unprecedented catalytic efficiency in visible-light-driven CO₂ reduction with an up to 3.25% apparent quantum yield and 90.3% CO selectivity, superior to most of the state-of-the-art photocatalysts under comparable conditions. More importantly, the Fe-CoP HDSNC is also highly effective under diluted CO₂ atmosphere, suggesting the practicability of the present photocatalytic system.

Dye-Sensitized Fe-MOF nanosheets as Visible-Light driven photocatalyst for high efficient photocatalytic CO2 reduction

Dye-sensitized system holds great potential for the development of visible-light-responsive photocatalysts not only because it can enhance the light absorption and charge separation efficiency of the systems but also because it can tune the band structure of catalysts. Herein, two-dimensional (2D) Fe-MOF nanosheets (Fe-MNS) with a LUMO potential of 0.11 V (vs. RHE) was prepared. Interestingly, it has been found that when the 2D Fe-MNS catalyst was functionalized with visible-light-responsive [Ru(bpy)]₃²⁺ as a dye-sensitizer, the electrons from the [Ru(bpy)]₃²⁺ can effectively inject into the 2D Fe-MNS, which resulted in a negative shift of the LUMO potential of the 2D Fe-MNS to -0.15 V (vs. RHE). Consequently, the [Ru(bpy)]₃²⁺/Fe-MNS catalytic system exhibits a sound photocatalytic CO₂-to-CO activity of 1120 μmol g^-1h^-1 under visible-light-irradiation. The photocatalytic CO production was further ameliorated by regulating the electronic structure of the 2D Fe-MNS by doping Co ions, achieving a remarkable photocatalytic activity of 1637 μmol g^-1h^-1. This work further supports that the dye-sensitized system is an auspicious strategy worth exploring with different catalysts for the development of visible-light-responsive photocatalytic systems.

Fe2TiO5/Fe2O3 (Shell/Shell) and (Shell/Core) Heterostructured for Efficient Oxygen Evolution

A delicate synthesis strategy of Fe₂TiO₅/Fe₂O₃ (shell/shell (s/s)) and (shell/core (s/c)) heterostructures was proposed to realize efficient photocatalytic water oxidation. The hierarchical structure increases the light absorption depth of material, the strongly coupled components promoted the separation of photoinduced excitons, and the high surface area with adequate porosity allowed the diffusion of electrolyte to adsorb at rich active sites. Furthermore, Fe₂TiO₅/Fe₂O₃ (s/s) was coated by graphitic carbon nitride (g-CN) subunits and exhibited good photocatalytic water reduction, resulting from the contact interface accelerating the effective separation of electrons and holes.

Converting Organic Wastewater into CO Using MOFs-Derived Co/In2O3 Double-Shell Photocatalyst

The photocatalytic conversion of organic wastewater into value-added chemicals is a promising strategy to solve the environmental issue and energy crisis. Herein, Co/In₂O₃ nanotubes with a double-shell structure, as a highly efficient photocatalyst, are synthesized by a one-step calcination method. The Co/In₂O₃ heterostructure shows an outstanding photocatalytic CO₂ reduction performance of 4902 μmol h^-1 g^-1. Notably, these Co/In₂O₃ photocatalysts also achieve CO₂ self-generation and in situ reduction conversion in acid organic wastewater (phenol solution), in which the high CO₂ (47.5 μmol h^-1 g^-1) and CO (0.9 μmol h^-1 g^-1) evolution rates are demonstrated under solar irradiation. Transient photovoltage (TPV) tests demonstrate that Co nanoparticles on Co/In₂O₃ double-shell heterostructure serve as the CO₂ reduction sites for the effective capture and stabilization of the photogenerated electrons.

Microbial fuel cells for remediation of environmental pollutants and value addition: Special focus on coupling diatom microbial fuel cells with photocatalytic and photoelectric fuel cells

With the advent of global industrialisation and adaptation of smart life there is rise in anthropogenic pollution especially in water. Remediation of the pollutants (such as metals, and dyes) present in industrial effluents is possible via microbes and algae present in the environment. Microbes are used in a microbial fuel cell (MFC) for remediation of various organic and inorganic pollutants. However, for industrial scale application coupling the MFCs with photocatalytic and photoelectric fuel cell has a potential in improving the output of power. It can also be used for remediation of pollutants more expeditiously, conserving fossil fuels, cleaning environment, hence making the coupled hybrid fuel cell to run economically. Furthermore, such MFC inbuilt with algae in living or powder form give additional value addition products like biofuel, polysaccharides, biopolymers, and polyhydroxy alkanoates etc. This review provides bird's eye view on the removal of environmental pollutants by different biological sources like bacteria and algae. The article is focussed on diatoms as potential algae since they are rich source of crude oil and high value added products in a hybrid photocatalytic MFC. It also covers bottle necks, challenges and future in this field of research.

A Renewable Light-Promoted Flexible Li-CO2 Battery with Ultrahigh Energy Efficiency of 97.9

Directly converting and storing abundant solar energy in next-generation energy storage devices is of central importance to build a sustainable society. Herein, a new prototype of a light-promoted rechargeable and flexible Li-CO₂ battery with a TiO₂ /carbon cloth (CC) cathode is reported for the direct utilization of solar energy to promote the kinetics of the carbon dioxide reduction reaction and carbon dioxide evolution reaction (CO₂ ER). Under illumination, photoelectrons are generated in the conduction band of TiO₂ /CC, followed by the enhancing diffusion of electrons and lithium ions during the discharge process. The photoelectrons on the cathode surface can regulate the morphology of the discharge product Li₂ CO₃ , contributing to boosting the kinetics of the subsequent CO₂ ER process. In the reverse charge process, photogenerated holes can favor the decomposition of Li₂ CO₃ , leading to a negative charge potential of 2.88 V without increased polarization over ≈60 h of cycling. Owing to an ultralow overpotential of 0.06 V between the discharge and charge process, an ultrahigh energy efficiency of 97.9% is attained under illumination. The introduction of a light-promoted flexible Li-CO₂ battery can pave the way toward developing the use of solar energy to address the charging overpotential of conventional Li-CO₂ batteries.

Synthesis and Applications of Nanostructured Hollow Transition Metal Chalcogenides

Nanostructures with well-defined structures and rich active sites occupy an important position for efficient energy storage and conversion. Recent studies have shown that a transition metal chalcogenide (TMC) has a unique structure, such as diverse structural morphology, excellent stability, high efficiency, etc., and is used in the fields of electrochemistry and catalysis. The nanohollow structure metal chalcogenide has broad application prospects due to the existence of a large number of active sites and a wide internal space, allowing a large number of ions and electrons to be transported. Summarizing synthetic strategies of nanostructured hollow transition metal sulfides (HTMC) and their applications in the field of energy storage and conversion is discussed here. Through some representative examples, the fabrication and properties of various hollow structures are analyzed, which prompt some emerging nanoengineering designs to be applied to transition metal chalcogenides. It is hoped that the construction of the HTMC will lead to a deeper understanding for the further exploration of energy storage and conversion.

NIR-Triggered Multi-Mode Antitumor Therapy Based on Bi2 Se3 /Au Heterostructure with Enhanced Efficacy

Of all the reaction oxygen species (ROS) therapeutic strategies, NIR light-induced photocatalytic therapy (PCT) based on semiconductor nanomaterials has attracted increasing attention. However, the photocatalysts suffer from rapid recombination of electron-hole pairs due to the narrow band gaps, which are greatly restricted in PCT application. Herein, Bi₂ Se₃ /Au heterostructured photocatalysts are fabricated to solve the problems by introducing Au nanoparticles (NPs) in situ on the surface of the hollow mesoporous structured Bi₂ Se₃ . Owing to the lower work function of Au NPs, the photo-induced electrons are easier to transfer and assemble on their surfaces, resulting in the increased separation of the electron-hole pairs with efficient ROS generation. Besides, Bi₂ Se₃ /Au heterostructures also enhance the photothermal efficiency due to the effective orbital overlaps with accelerated electron migrations according to density functional theory calculations. Moreover, the PLGA-PEG and the doxorubicin (DOX) are introduced for photothermal-triggered drug release in the system. The Bi₂ Se₃ /Au heterostructures also displays excellent infrared thermal (IRT) and computed tomography (CT) dual-modal imaging property for promising cancer diagnosis. Collectively, Bi₂ Se₃ /Au@PLGA-PEG-DOX exhibits prominent tumor inhibition effect based on synchronous PTT, PCT and chemotherapy triggered by NIR light for efficient antitumor treatment.

Efficient Electrochemical Production of H2O2 on Hollow N-Doped Carbon Nanospheres with Abundant Micropores

Electrocatalytic two-electron (2e-) oxygen reduction reaction (ORR) has been regarded as an efficient strategy to achieve onsite H2O2 generation under ambient conditions. However, due to the sluggish kinetics and competitive reaction between 2e- and 4e- ORR, exploring more efficient ORR catalysts with dominant 2e- ORR selectivity is of significance. Herein, hollow N-doped carbon spheres (HNCS) with abundant micropores through a template-directed method are presented. Consequently, the selectivity of the HNCS reaches ∼91.9% at 0.7 V (vs RHE), and the output for H2O2 production is up to 618.5 mmol gcatalyst-1 h-1 in 0.1 M KOH solution. The enhanced performance of HNCS for H2O2 electrosynthesis could be attributed to the hollow structure and heteroatom/defect/pore incorporation. The strategy presented here could shed light on the design of efficient carbon-based materials for improved 2e- ORR.

Universal MOF-Mediated synthesis of 2D CoNi-based layered triple hydroxides electrocatalyst for efficient oxygen evolution reaction

Developing low-budget, stable, and high-performance electrocatalyst toward oxygen evolution reaction (OER) is of pivotal significance in the fields of energy conversion and storage. Herein, a universal metal organic framework (MOF)-mediated method for the synthesis of two-dimensional (2D) layered triple hydroxides (LTHs) nanosheets with ultrathin nature has been developed. It is interesting to disclose that the CoNi-based LTHs possess better electrochemical catalytic performance, giving superior performance to commercial RuO₂ catalysts. Remarkably, benefitting from the ultrathin nanosheet configuration, optimized electronic structure, and strong synergistic effect, the optimized CoNiFe LTHs nanosheets show excellent OER performance with an ultralow overpotential of 262 mV at a current density of 10 mA cm^-2 and a small Tafel slope of 88.1 mV dec^-1. This work provides a promising avenue to develop low-cost and high-performance layered ternary hydroxide electrocatalysts.

Yolk-Shelled Gold@Cuprous Oxide Nanostructures with Hot Carriers Boosting Photocatalytic Performance

Plasmonic Au nanoparticles (NPs) have been commonly used to enhance the photocatalytic activity of Cu₂O. Till now, core-shell Au NP@Cu₂O composites have been reported in previous studies. Yet, these Au@Cu₂O composites only exhibit visible light response. Other special Au nanostructures, such as Au nanorods (NRs) or Au nanobipyramids (NBPs), which possess near-infrared light absorption, were rarely used to endow the near-infrared light response for Cu₂O. In this work, for the first time, we used Au NPs, Au NRs, and Au NBPs and employed a handy and universal method to synthesize a series of yolk-shelled Au@Cu₂O composites. The results showed that the yolk-shelled Au@Cu₂O composites had much higher photocatalytic activity than their solid-shelled ones and pure Cu₂O. More importantly, yolk-shelled Au NR@Cu₂O and Au NBP@Cu₂O composites indeed presented excellent near-infrared light-driven photocatalytic activity, which were impossible for Au NP@Cu₂O and pure Cu₂O. This outstanding performance for yolk-shelled Au NR@Cu₂O and Au NBP@Cu₂O could be attributed to the transfer of abundant hot electrons from Au NRs or Au NBPs to Cu₂O, and the timely utilization of hot holes on Au through the rich pore channels on their yolk-shelled structure. Furthermore, yolk-shelled Au@Cu₂O also showed better stability than pure Cu₂O, owing to the migration of the oxidizing holes from Cu₂O to Au driven by the built-in electric field. This work may give a guide to fabricate controllable and effective photocatalysts based on plasmonic metals and semiconductors with full solar light-driven photocatalytic activities in the future.