A photocatalytic redox cycle over a polyimide catalyst drives efficient solar-to-H2O2 conversion.

Circumventing the conventional two-electron oxygen reduction pathway remains a great problem in enhancing the efficiency of H2O2 photosynthesis. A promising approach to achieve outstanding photocatalytic activity involves the utilization of redox intermediates. Here, we engineer a polyimide aerogel photocatalyst with photoreductive carbonyl groups for non-sacrificial H2O2 production. Under photoexcitation, carbonyl groups on the photocatalyst surface are reduced, forming an anion radical intermediate. The produced intermediate is oxidized by O2 to produce H2O2 and subsequently restores the carbonyl group. The high catalytic efficiency is ascribed to a photocatalytic redox cycle mediated by the radical anion, which not only promotes oxygen adsorption but also lowers the energy barrier of O2 reduction reaction for H2O2 generation. An apparent quantum yield of 14.28% at 420 ± 10 nm with a solar-to-chemical conversion efficiency of 0.92% is achieved. Moreover, we demonstrate that a mere 0.5 m2 self-supported polyimide aerogel exposed to natural sunlight for 6 h yields significant H2O2 production of 34.3 mmol m-2.

Boosting H2O2 generation by shortening the charge migration distance in BiPO4 nanocrystals.

The photocatalytic production of H2O2 has gained recognition as an economical and eco-friendly technology, but it suffers from limitations such as low production rates and difficulty in achieving high concentrations. This study was designed to overcome these limitations by preparing BiPO4 nanocrystals (BIP NCs) via high-temperature hydrolysis, and X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that BIP NCs with particle sizes of 8.5 ± 3 nm were synthesized. In a photocatalytic performance test, only H2O and O2 were used to produce H2O2, resulting in an accumulation of H2O2 of up to 30.44 mM·g-1, as measured with the potassium titanium oxalate method; this value was 3.13 times greater than that of bulk BiPO4 (BIP-B). The resulting nanocrystals demonstrated superior electron-hole transport and separation efficiency compared to those of BIP-B, and H2O2 was formed in a one-step two-electron process. Furthermore, a film composed of a gas diffusion layer (GDL) and BIP NCs provided continuous accumulation of H2O2; a concentration of 7.23 mM was achieved after 96 h of reaction, and the stability of the film was confirmed by comparing scanning electron microscopy (SEM) images obtained before and after the reaction. Construction of a nanocrystalline structure to enhance the activities of photocatalysts and films and achieve continuous accumulation of H2O2 will provide insights into the photocatalytic production of highly concentrated H2O2.

Silver and Copper Dual Single Atoms Boosting Direct Oxidation of Methane to Methanol via Synergistic Catalysis.

Rationally constructing atom-precise active sites is highly important to promote their catalytic performance but still challenging. Herein, this work designs and constructs ZSM-5 supported Cu and Ag dual single atoms as a proof-of-concept catalyst (Ag1 -Cu1 /ZSM-5 hetero-SAC (single-atom catalyst)) to boost direct oxidation of methane (DOM) by H2 O2 . The Ag1 -Cu1 /ZSM-5 hetero-SAC synthesized via a modified co-adsorption strategy yields a methanol productivity of 20,115 µmol gcat -1 with 81% selectivity at 70 °C within 30 min, which surpasses most of the state-of-the-art noble metal catalysts. The characterization results prove that the synergistic interaction between silver and copper facilitates the formation of highly reactive surface hydroxyl species to activate the C-H bond as well as the activity, selectivity, and stability of DOM compared with SACs, which is the key to the enhanced catalytic performance. This work believes the atomic-level design strategy on dual-single-atom active sites should pave the way to designing advanced catalysts for methane conversion.

Z-scheme cobalt-iron oxide/perylene diimide supermolecule heterojunction for high-efficiency ciprofloxacin removal in a photocatalysis-self-Fenton system.

Fenton technology has been famous on antibiotics removal, but seriously restricted by the extra addition of H2O2 and low mineralization efficiency. Herein, we develop a novel cobalt-iron oxide/perylene diimide organic supermolecule (CoFeO/PDIsm) Z-scheme heterojunction under photocatalysis-self-Fenton system, in which the holes (h+) of photocatalyst can mineralize organic pollutants and the photo-generated electrons (e-) are used to in-situ H2O2 production with high efficiency. The CoFeO/PDIsm exhibits superior in-situ H2O2 production at a rate of 281.7 µmol g-1 h-1 in contaminating solution, correspondingly of total organic carbon (TOC) removal rate of ciprofloxacin (CIP) is 63.7 %, far exceeding current photocatalysts. The high H2O2 production rate and remarkable mineralization ability are ascribed to great charge separation in Z-scheme heterojunction. This work provides a novel Z-scheme heterojunction with photocatalysis-self-Fenton system for environmental-friendly removing the organic containment.

Coral-like B-doped g-C3N4 with enhanced molecular dipole to boost photocatalysis-self-Fenton removal of persistent organic pollutants.

Fenton process is a popular advanced oxidation process for water purification. However, it requires an external addition of H2O2, thus raising safety threats and economic costs and encountering the problems of slow cycling of Fe2+/Fe3+ and low mineralization efficiency. Herein, we developed a novel photocatalysis-self-Fenton system based on coral-like B-doped g-C3N4 (Coral-B-CN) photocatalyst for 4-chlorophenol (4-CP) removal where H2O2 can be in situ generated by photocatalysis over Coral-B-CN, the cycling of Fe2+/Fe3+ was accelerated by photoelectrons, and the photoholes promoted 4-CP mineralization. Coral-B-CN was innovatively synthesized by hydrogen bond self-assembly followed by calcination. B heteroatom doping produced enhanced molecular dipole, while the morphological engineering exposed more active sites and optimized band structure. The effective combination of the two enhances charge separation and mass transfer between the phases, resulting in efficient in-situ H2O2 production, faster Fe2+/Fe3+ valence cycling and enhanced hole oxidation. Accordingly, nearly all 4-CP can be degraded during 50 min under the combined action of more ·OH and holes with stronger oxidation capacity. The mineralization rate of this system reached 70.3%, which is 2.6 and 4.9 times higher than that of Fenton process and photocatalysis, respectively. Besides, this system maintained excellent stability and can be applied in a broad range of pHs. The study would provide important insights into developing improved Fenton process with high performance for the removal of persistent organic pollutants.

Photocatalysis-self-Fenton system over edge covalently modified g-C3N4 with high mineralization of persistent organic pollutants.

The Fenton process is a widely used to remedy organic wastewaters, but it has problems of adding H2O2, low utilization efficiency of H2O2 and low mineralization efficiency. Here, a new photocatalysis-self-Fenton process was exploited for the removal of persistent 4-chlorophenol (4-CP) pollutant through coupling the photocatalysis of 4-carboxyphenylboronic acid edge covalently modified g-C3N4 (CPBA-CN) with Fenton. In this process, H2O2 was in situ generated via photocatalysis over CPBA-CN, the photogenerated electrons assisted the accelerated regeneration of Fe2+ to improve the utilization efficiency of H2O2, and the photogenerated holes facilitated the enhancement of 4-CP mineralization. Under the conjugation of CPBA, the electronic structure of CN was optimized and the molecular dipole was enhanced, resulting in the deepening valence band position, accelerated electron-hole pair separation, and improved O2 adsorption-activation. Therefore, the incremental 4-CP degradation rate in the CPBA-CN photocatalysis-self-Fenton process was approaching 0.099 min-1, by a factor of 3.1 times compared with photocatalysis. The parallel mineralization efficiency increased to 74.6% that was 2.1 and 2.6 times than photocatalysis and Fenton, respectively. In addition, this system maintained an excellent stability in the recycle experiment and can be potentially applied in a wide range of pHs and under the coexistence of various ions. This study would provide new insights for improving Fenton process and promote further development of Fenton in organic wastewater purification.

Selectively Permeable FeOOH Amorphous Layer Coating CdS for Enhancing Photocatalytic Conversion of Benzyl Alcohol and Selectivity to Benzaldehyde.

The development of new strategies to improve reaction efficiency and light utilization is one of the biggest challenges in photosynthetic chemistry. Dynamics control, particularly tuning the adsorption/desorption of reactants and products, is an ideal way to improve the conversion and selectivity in catalytic reactions, but it is rarely studied for photocatalytic organic synthesis. This study concerns the design of an amorphous FeOOH coating to decorate CdS photocatalyst to control the adsorption and desorption of reactants and products to improve reaction efficiency for the photocatalytic conversion of benzyl alcohol (BA) into benzaldehyde (BAD). The best conversion of the core-shell photocatalyst is 74.1 % in 2 h, together with >99.9 % selectivity to BAD, and the photocatalyst exhibits response above 600 nm, which is the longest active wavelength reported for the reaction. Further data illustrate that the amorphous FeOOH coating enables selective sorption of BA/BAD molecules by H-bonding interactions, which may result in the excellent performance. Construction of amorphous coating layers and understanding the selective permeability may provide a new strategy for the design of more efficient photocatalytic systems for organic synthesis.

Aptamer-Based Fluorescence Detection and Selective Disinfection of Salmonella Typhimurium by Using Hollow Carbon Nitride Nanosphere.

Hollow carbon nitride nanosphere (HCNS) was synthesized via the hard template method to improve the fluorescence characteristics, drug delivery ability, and photocatalytic activity. Blue fluorescent HCNS was utilized as a quenching agent and an internal reference to combine with Cy5-labelled aptamer (Cy5-Apt), resulting in an off-on fluorescence aptasensing method for the detection of Salmonella typhimurium (S. typhimurium). Under optimum conditions, this fluorescence assay presented a linear range from 30 to 3 × 104 CFU mL-1 with a detection limit of 13 CFU mL-1. In addition, HCNS was also used as a drug carrier to load chloramphenicol (Cap) molecules. The Cap-loading amount of HCNS could reach 550 µg mg-1 within 24 h, whereas the corresponding Cap-release amount is 302.5 µg mg-1 under acidic and irradiation conditions. The integration of photocatalyst with antibiotic could endow HCNS-Cap with better disinfection performance. The bactericidal efficiency of HCNS-Cap (95.0%) against S. typhimurium within 12 h was better than those of HCNS (85.1%) and Cap (72.9%). In addition, selective disinfection of S. typhimurium was further realized by decorating aptamer. Within 4 h, almost all S. Typhimurium were inactivated by HCNS-Cap-Apt, whereas only 13.3% and 48.2% of Staphylococcus aureus and Escherichia coli cells were killed, respectively. Therefore, HCNS is a promising bio-platform for aptamer-based fluorescence detection and selective disinfection of S. typhimurium.

CO2 Electroreduction to Formate at a Partial Current Density up to 590 mA mg-1 via Micrometer-Scale Lateral Structuring of Bismuth Nanosheets.

2D bismuth nanosheets are a promising layered material for formate-producing via electrocatalytic CO2 conversion. However, the commercial interest of bismuth nanosheets in CO2 electroreduction is still rare due to the undesirable current density for formate at moderate operation potentials (about 200 mA mg-1 ) and harsh synthesis conditions (high temperature and/or high pressure). This work reports the preparation of Bi nanosheets with a lateral size in micrometer-scale via electrochemical cathodic exfoliation in aqueous solution at normal pressure and temperature. As-prepared Bi LNSs (L indicates large lateral size) possess high Faradaic efficiencies over 90% within a broad potential window from -0.44 to -1.10 V versus RHE and a superior partial current density about 590 mA mg-1 for formate in comparison with state-of-the-art results. Structure analysis, electrochemical results, and density functional theory calculations demonstrate that the increasing tensile lattice strain observed in Bi LNSs leads to less overlap of d orbitals and a narrower d-band width, which tuning the intermediate binding energies, and therefore promotes the intrinsic activity.

Efficient interfacial charge transfer of 2D/2D porous carbon nitride/bismuth oxychloride step-scheme heterojunction for boosted solar-driven CO2 reduction.

Heterostructured photocatalysts are promising candidates in the photocatalysis field, and the heterojunction plays a vital role in the separation of spatial charge carriers. Here, a heterojunction was fabricated by the in situ growth of ultrathin Bi12O17Cl2 (BOC) nanosheets (NSs) onto porous g-C3N4 (PGCN) NSs. The NSs' nanostructure can effectively shorten the diffusion path of charge carriers and thus promote interfacial charge migration, which can improve the surface photocatalytic activity. The X-ray photoelectron spectroscopy spectra and the experimental measured Fermi level (EF) indicate that electrons transfer from PGCN to BOC, which leads to the formation of the built-in electric field with the orientation from PGCN to BOC. Driven by the built-in electric field, the charge carriers transfer through a step-like pathway. This step-scheme porous g-C3N4/Bi12O17Cl2 (PGCN/BOC) heterostructured nanocomposite displays an enhanced photocatalytic performance compared with pure BOC and PGCN. This work provides new insight into the novel construction of a step-scheme heterojunction toward photocatalytic CO2 reduction.

Overall Water Splitting on the Transition-Metal Oxynitride Photocatalyst LaMg1/3Ta2/3O2N over a Large Portion of the Visible-Light Spectrum.

One of the main targets of studies on water splitting photocatalysts is to develop semiconductor materials with narrower bandgaps capable of overall water splitting for efficient harvesting of solar energy. A series of transition-metal oxynitrides, LaMgx Ta1-xO1+3xN2-3x(x ≥ 1/3), with a complex perovskite structure was reported as the first example of overall water splitting operable at up to 600 nm. The photocatalytic behavior of LaMg1/3Ta2/3O2N was investigated in detail in order to optimize photocatalyst preparation and water-splitting activity. Various attempts exploring photocatalyst preparation steps, that is, cocatalyst selection, coating material and method, and synthesis method for the oxide precursor, revealed photocatalyst structures necessary for achieving overall water splitting. Careful examination of photocatalyst preparation procedures likely enhanced the quality of the produced photocatalyst, leading to a more homogeneous coating quality and semiconductor particles with fewer defects. Thus, the photocatalytic activity for water splitting on LaMg1/3Ta2/3O2N was largely enhanced.

Fabrication of a Core-Shell-Type Photocatalyst via Photodeposition of Group IV and V Transition Metal Oxyhydroxides: An Effective Surface Modification Method for Overall Water Splitting.

The design of optimal surface structures for photocatalysts is a key to efficient overall water splitting into H2 and O2. A unique surface modification method was devised for a photocatalyst to effectively promote overall water splitting. Photodeposition of amorphous oxyhydroxides of group IV and V transition metals (Ti, Nb, Ta) over a semiconductor photocatalyst from corresponding water-soluble metal peroxide complexes was examined. In this method, amorphous oxyhydroxide covered the whole surface of the photocatalyst particles, creating a core-shell structure. The water splitting behavior of the novel core-shell-type photocatalyst in relation to the permeation behavior of the coating layer was investigated in detail. Overall water splitting proceeded successfully after the photodeposition, owing to the prevention of the reverse reaction. The photodeposited oxyhydroxide layers were found to function as molecular sieves, selectively filtering reactant and product molecules. By exploiting the selective permeability of the coating layer, redox reactions on the photocatalyst surface could be suitably controlled, which resulted in successful overall water splitting.

Photocatalytic overall water splitting on the perovskite-type transition metal oxynitride CaTaO2N under visible light irradiation.

Overall water splitting was achieved on a simple perovskite oxynitride photocatalyst, CaTaO2N, with an absorption edge at 510 nm. This photocatalyst, modified with a Rh-Cr bimetallic oxide cocatalyst, produced stoichiometric H2 and O2 steadily under UV and visible light irradiation after coating of the photocatalyst particles with amorphous Ti oxyhydroxide.

A complex perovskite-type oxynitride: the first photocatalyst for water splitting operable at up to 600†nm.

One of the simplest methods for splitting water into H2 and O2 with solar energy entails the use of a particulate-type semiconductor photocatalyst. To harness solar energy efficiently, a new water-splitting photocatalyst that is active over a wider range of the visible spectrum has been developed. In particular, a complex perovskite-type oxynitride, LaMg(x)Ta(1-x)O(1+3x)N(2-3x)(x≥1/3), can be employed for overall water splitting at wavelengths of up to 600 nm. Two effective strategies for overall water splitting were developed. The first entails the compositional fine-tuning of a photocatalyst to adjust the bandgap energy and position by forming a series of LaMg(x)Ta(1-x)O(1+3x)N(2-3x) solid solutions. The second method is based on the surface coating of the photocatalyst with a layer of amorphous oxyhydroxide to control the surface redox reactions. By combining these two strategies, the degradation of the photocatalyst and the reverse reaction could be prevented, resulting in successful overall water splitting.

Recent progress in oxynitride photocatalysts for visible-light-driven water splitting.

Photocatalytic water splitting into hydrogen and oxygen is a method to directly convert light energy into storable chemical energy, and has received considerable attention for use in large-scale solar energy utilization. Particulate semiconductors are generally used as photocatalysts, and semiconductor properties such as bandgap, band positions, and photocarrier mobility can heavily impact photocatalytic performance. The design of active photocatalysts has been performed with the consideration of such semiconductor properties. Photocatalysts have a catalytic aspect in addition to a semiconductor one. The ability to control surface redox reactions in order to efficiently produce targeted reactants is also important for photocatalysts. Over the past few decades, various photocatalysts for water splitting have been developed, and a recent main concern has been the development of visible-light sensitive photocatalysts for water splitting. This review introduces the study of water-splitting photocatalysts, with a focus on recent progress in visible-light induced overall water splitting on oxynitride photocatalysts. Various strategies for designing efficient photocatalysts for water splitting are also discussed herein.

Core/Shell photocatalyst with spatially separated co-catalysts for efficient reduction and oxidation of water.

A simple method allows the preparation of core/shell photocatalysts with spatially separated co-catalysts for efficient water splitting. The high activity was attributed to the core/shell structure and separated co-catalysts that assisted separation and collection of the electrons and holes at the respective co-catalysts, owing to active rectification of electron and hole transport (see picture; Eg =2.1 eV).

New type of BiPO(4) oxy-acid salt photocatalyst with high photocatalytic activity on degradation of dye.

A high photocatalytic BiPO(4) with a novel nonmetal oxy acid structure is synthesized by a hydrothermal method. BiPO(4) photocatalyst has an optical indirect band gap of 3.85 eV. In a comparison of BiPO(4) with that of TiO(2) (P25, Degussa), it is found that the photocatalytic activity of BiPO(4) is twice that of TiO(2) (P25, Degussa) for the degradation of methylene blue (MB) dye, while the BET surface of BiPO(4) is just one tenth of that of P25. Both the high position of the valence band and the high separation efficiency of electron-hole pairs result in the high photocatalytic activity. The inductive effect of PO(4)(3-) helps the e(-)/h(+) separation, which plays an important role in its excellent photocatalytic activity. It may extend to the synthesis of other inorganic nonmetal salts of oxy photocatalysts with suitable band gap and high activity for the environmental purification of organic pollutants in aqueous solution.

Synthesis of CeO2 nanorods via ultrasonication assisted by polyethylene glycol.

Polycrystalline CeO2 nanorods 5-10 nm in diameter and 50-150 nm in length were synthesized via ultrasonication using polyethylene glycol (PEG) as a structure-directing agent at room temperature. The properties of the CeO2 nanorods were characterized by TEM, EDS, XRD, XPS, FT-IR, TG, BET, and UV-vis spectroscopy. Various reaction parameters, such as the content of PEG, the molecular weight of PEG, the concentration of KOH, the pH value, and the sonication time, were investigated by a series of control experiments. The content of PEG, the molecular weight of PEG, and the sonication time were confirmed to be the crucial factors determining the formation of one-dimensional CeO2 nanorods. A possible ultrasonic formation mechanism has been suggested to explain the formation of CeO2 nanorods.