Improved Charge Carrier Separation Research Articles

Eco-friendly synthesis and surface modification of ZnO nanoparticles using Pueraria montana root extract: enhanced photocatalytic performance with trisodium pyrophosphate

ABSTRACT The synthesis of zinc oxide (ZnO) nanoparticles using Pueraria montana (kudzu) plant extracts highlights advancements in green nanotechnology. This study explores the use of Pueraria montana roots, rich in phytochemicals such as phenols, terpenoids and flavonoids, which serve as natural reducing and stabilizing agents for nanoparticle synthesis. The eco-friendly production and surface modification of ZnO nanoparticles were achieved using these plant extracts, enhancing their photocatalytic performance with trisodium pyrophosphate (TSPP).Characterization techniques, including XRD, TEM, and FE-SEM, confirmed the nanoparticles’ crystalline structure, with a BET surface area of 14.01 m²/g and a type II adsorption isotherm. The synthesized nanoparticles exhibited exceptional dye degradation capabilities, achieving 99.9% removal of malachite green (MG) and 97.78% for aniline blue (AB). Kinetic analysis revealed a steady-state rate constant (k) of 2 × 10⁻⁴ min⁻¹ for MG where as the response rate constant(k) for the photocatalytic degradation of AB using modified ZnO nanostructures was 3.0 × 10−3 min−1 allowing near-total dye removal within 600 minutes for MG and 350 min for AB . Adsorption studies were well described by Langmuir and Freundlich isotherms, indicating maximum adsorption capacities of 59.7 mg/g for MG and 61.2 mg/g for AB. Surface modification with TSPP improved charge carrier separation and enhanced the generation of reactive oxygen species under UV exposure, further increasing dye degradation efficiency.Statistical analysis indicated high reproducibility, with close mean adsorption values of 99.125 for MG and 97.3125 for AB, supported by small standard deviations. The findings affirm the potential of using Pueraria montana in synthesizing efficient photocatalysts, providing a sustainable and cost-effective approach for water treatment applications. Overall, this research underscores the effectiveness of plant-based materials in advancing eco-friendly nanotechnology solutions.

Aqueous glass-coated CsPbI3 quantum dots implanted in g-C3N4 nanosheets for efficient photocatalytic water splitting and H2O2 generation

Increasing visible light harvesting and improving charge carrier separation and transfer efficiency are crucial for photocatalytic H2O2 generation using graphitic carbon nitrides (g-C3N4) based catalysts. In this paper, a high temperature solid synthesis was developed to create water stable SiO2 glass coated CsPbI3 (CsPbI3@SiO2) quantum dots (QDs) with high brightness and extraordinary stability. These CsPbI3@SiO2 QDs were implanted in superior thin g-C3N4 nanosheets via a solvothermal synthesis. The red-emission of CsPbI3 QDs and the blue emission of g-C3N4 nanosheets were quenched after incorporation to confirm that photogenerated electron transition occurred. The further polymerization of g-C3N4 during solvothermal treatment resulted in CsPbI3@SiO2/g-C3N4 with well-developed interface to improve the charge transfer efficiency. A type II heterostructure formed after CsPbI3@SiO2 QDs incorporated with g-C3N4 nanosheets. The heterostructure revealed enhanced photocatalytic H2 and H2O2 generation, in which the evolution rate of H2O2 was 2454.4 μmol·g−1·h−1 while the photocatalytic H2 generation rate was 2463.1 μmol·g−1·h−1. The mechanism test indicated that the photocatalytic production of H2O2 was carried through a two-step single-electron redox process. Superoxide radicals were important intermediates for the generation of H2O2. This study provides a new scheme for the preparation of g-C3N4 based heterojunction photocatalyst for efficient photocatalytic production of H2O2 and H2.

Bioinspired copper oxide nanocomposites: harnessing plant extracts for enhanced photocatalytic performance.

This study focuses on developing copper oxide-based nanocomposites using plant extracts for photocatalytic applications. Curcuma amada leaf and Alysicarpus vaginalis leaf extracts were utilized alongside recycled copper precursors to synthesize photocatalysts via a green synthesis approach. Structural characterization through X-ray diffraction confirmed the formation of monoclinic CuO with reduced crystallite sizes due to plant extract incorporation. Fourier-transform infrared spectroscopy identified additional functional groups from the plant extracts, enhancing the material's properties. UV-Vis spectroscopy demonstrated increased light absorption and narrowed bandgaps in the nanocomposites, crucial for efficient photocatalysis under visible light. Morphological studies using FESEM revealed unique leaf-like structures in nanocomposites, indicative of the plant extract's influence on morphology. Photocatalytic degradation of methylene blue, rhodamine B, Congo red, and reactive blue 171 dyes showed enhanced performance of plant extract-modified CuO compared to without plant extract mediated CuO, attributed to improved charge carrier separation and extended lifetime. The effects of pH, catalyst dosage, and dye concentration on degradation efficiency were systematically investigated, highlighting optimal conditions for each dye type. Radical scavenger studies confirmed the roles of holes and hydroxyl radicals in the degradation process. Kinetic analysis revealed pseudo-second-order kinetics for dye degradation, underscoring the effectiveness of the nanocomposites. Overall, this research provides insights into sustainable photocatalytic materials using plant extracts and recycled copper, showcasing their potential for environmental remediation applications.

Charge Redistribution in Nise2/Mos2 n–n Heterojunction Towards the Photoelectrocatalytic Degradation of Ciprofloxacin

AbstractThis study reports the photoelectrocatalytic (PEC) activity of a n–n heterojunction comprising MoS2 and NiSe2. The synthesis of the composite was achieved through a facile solvothermal method, yielding an exfoliated MoS2 layered sheet loaded with NiSe2 nanoparticles. Under visible light radiation and an external electric field, the obtained composite NiSe2/MoS2 exhibited enhanced catalytic activity for ciprofloxacin (CIP) degradation. The NiSe2/MoS2 heterojunction achieved about 78 % degradation efficiency with a first‐order kinetic rate of 0.0111 min−1, compared to 38 % efficiency and a first‐order kinetic rate of 0.0044 min−1 observed for MoS2. The NiSe2/MoS2 heterojunction was more advantageous due to the synergy of charge carrier induction by visible light radiation and improved charge carrier separation induced by the external electric field. The formation of n–n heterojunction at the interface of the two materials resulted in charge redistribution in the materials, with a simultaneous realignment of the band structure to achieve Fermi energy equilibration. The primary reactive species responsible for CIP degradation was identified as the photo‐induced h+. Furthermore, the catalyst exhibited high stability and reusability, with no significant reduction in activity observed after five experimental cycles. This study reveals the potential of exploring the synergy between the photocatalytic and electrocatalytic processes in removing harmful pharmaceutical compounds from water.

Thienyl-fused dibenzothiophene-S,S-dioxide based conjugated polymer toward highly efficient photocatalytic hydrogen production

Dibenzothiophene-S,S-dioxide (BTDO) is one of the cutting-edge electron-acceptor monomers for designing conjugated polymer based organic materials toward photocatalytic H2 production from water. Normally, structure design of BTDO containing donor-acceptor (D-A) polymer photocatalyst mainly focuses on screening electron-donor motifs, the importance of modification on BTDO molecular toward improving charge carrier separation and photocatalytic performance is always ignored. Herein, a novel thienyl-fused BTDO building block (BTDO-DT) is prepared and utilized to synthesize B-BTDO-DT polymer photocatalyst by Sonogashira-Hagihara cross-coupling polycondensation using 1,4-Diethynylbenzene (B) and BTDO-DT as monomers. Experimental and density functional theory (DFT) calculation results demonstrate that modification of BTDO by thiophene not only enlarges light absorption region and promotes photogenerated e−/h+ separation, but also decreases H atom adsorption free energy (ΔGH*) on oxygen atom in the OSO group. As a result, B-BTDO-DT exhibits an outstanding visible light induced photocatalytic H2 production rate of 156.6 μmol h−1 using 30 mg catalyst without Pt cocatalyst, which is 4.5 times higher than that of B-BTDO. And the H2 production rate of B-BTDO-DT is further improved to be 259.8 μmol h−1 with 2.0 wt% Pt as co-catalyst. The present work may open a new direction for the design of conjugated polymer based photocatalysts with high photocatalytic activities.

MoO3 with the Synergistic Effect of Sulfur Doping and Oxygen Vacancies: The Influence of S Doping on the Structure, Morphology, and Optoelectronic Properties.

Molybdenum trioxide (MoO3) is an attractive semiconductor. Thus, bandgap engineering toward photoelectronic applications is appealing yet not well studied. Here, we report the incorporation of sulfur atoms into MoO3, using sulfur powder as a source of sulfur, via a self-developed hydrothermal synthesis approach. The formation of Mo-S bonds in the MoO3 material with the synergistic effect of sulfur doping and oxygen vacancies (designated as S-MoO3-x) is confirmed using Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR). The bandgap is tuned from 2.68 eV to 2.57 eV upon sulfur doping, as confirmed by UV-VIS DRS spectra. Some MoS2 phase is identified with sulfur doping by referring to the photoluminescence (PL) spectra and electrochemical impedance spectroscopy (EIS), allowing significantly improved charge carrier separation and electron transfer efficiency. Therefore, the as-prepared S-MoO3-x delivers a sensitive photocurrent response and splendid cycling stability. This study on the synergistic effect of sulfur doping and oxygen vacancies provides key insights into the impact of doping strategies on MoO3 performance, paving new pathways for its optimization and development in relevant fields.

Enhancing Photocatalytic Activity for Solar‐to‐Fuel Conversion: A Study on S‐Scheme AgInS2/CeVO4@Biocharx Heterojunctions

AbstractRare earth vanadates are promising for solar‐to‐fuel conversions, yet their photocatalytic efficiency is limited by the substantial recombination of photo‐generated carriers. Constructing heterojunctions is recognized as an effective approach to improving charge carrier separation in vanadates. Nonetheless, inefficient charge transfer often results from the poor quality of interfaces and non‐directional charge transfer within these heterojunctions. Herein, an S‐scheme AgInS2/CeVO4@Biocharx (AIS/CV@Cx) heterojunction photocatalyst is designed and synthesized through a straightforward freeze‐drying and calcination three‐step process, aimed at photocatalytic co‐production of xylonic acid and carbon monoxide (CO) from xylose. The AIS/CV@C2 heterojunction achieves an optimal yield of 67.74% for xylonic acid and a CO release of 29.76 µmol from xylose. The enhanced photocatalytic performance of the AIS/CV@C2 heterojunction is attributed to three key factors: I) the high‐quality interface and intimate contact within the AIS/CV@C2 heterojunction significantly reduce undesirable carriers recombination, II) the staggered band structures and directed carriers transfer in the AIS/CV@C2 heterojunction notably improve spatial carriers separation/migration, and III) the incorporation of biochar boosts the conductivity of the AIS/CV@C2 heterojunction. This work presents a straightforward yet effective method for fabricating vanadate heterojunctions, highlighting the importance of quality interfacial contact and directed charge transfer in amplifying photocatalytic performance.

Enhanced synergistic removal of tetracycline and uranium in wastewater using Defective-Enriched S-scheme hollow dodecahedron K3PW12O40@WS2 heterojunction

In aquatic environments, the coexistence and interaction of multiple the pollutants complicate remediation process. This study focuses on developing a defective-enriched S-scheme heterojunction of K3PW12O40@WS2 (KPW@WS2) with hollow structure for the simultaneous removal of tetracycline (TC) and hexavalent uranium (U(VI)) in wastewater. The internal electric field (IEF) within this heterojunction plays a crucial role in efficiently separating photo-generated carriers, creating high reduction and oxidation active sites. The band structure and optical properties suggest that WS2-Vs have a narrower band gap energy compared to conventional WS2, leading to improved charge carrier separation and transfer rates. Density functional theory (DFT) calculations support the reduced recombination of electron-hole pairs in WS2-Vs due to the presence of S vacancies. Experimental results reveal a synergistic effect between the removal of TC and U(VI), with a significant increase in the reaction rate constant for the reduction of U(VI) to 0.0426 min−1, 1.6 times higher than in a single U(VI) reduction system. Additionally, the reaction rate constant for the oxidation of TC also rises from 0.0573 to 0.0729 min−1. The study also delves into the photocatalytic mechanism, degradation pathways, and intermediate products. Overall, this research offers an innovative strategy for simultaneous pollutant removal and optimizing photocatalytic redox reactions to enhance solar energy utilization.

Selective photochemical oxidation of sulfides by Gallium and Sulfur Co-Modified TiO2/g-C3N4 Nanocomposites as catalyst

In this study, with the objective of promoting the oxidation of sulfides, a distinctive photocatalyst was synthesized by incorporating Ga- and S-co-doped TiO2 onto graphitic carbon nitride (g-C3N4). Under visible light irradiation, the composites demonstrated enhanced photocatalytic performance in comparison to g-C3N4 and TiO2/g-C3N4. The nanocomposite catalyst displayed a remarkable enhancement in photocatalytic activity, benefiting from the creation of a Z-scheme heterojunction by combining TiO2 and g-C3N4, as well as the presence of electron trap centers, efficient photogenerated electron transfer, improved charge carrier separation, and extended optical absorption in the visible light range. To optimize the performance, the substitution contents of Ga and S (GaxSy@TiO2-g-C3N4) were varied, where the values of x and y were set at 5 % and 10 %, respectively. Notably, Based on the obtained results, it was observed that the Ga5.0S10.0@TiO2-g-C3N4 sample displayed the highest yield when subjected to visible-light irradiation, making it the most effective and optimal sample. The findings of this study offer a fresh perspective on the synergistic effect of dopant photocatalysts in the oxidation of organic compounds. This work presents a novel approach for the development of highly efficient photocatalysts capable of effectively oxidizing organic compounds.

Interconnected Periodic Macroporous NaNbO3 for High-Efficiency Solar-Driven Photocatalytic Hydrogen Evolution.

Highly ordered periodic macroporous structures have been extensively utilized to significantly enhance the photocatalytic activity. However, constructing 3D interconnected ordered porous ternary nanostructures with highly crystalline frameworks remains a formidable challenge. Here, we introduce the design and fabrication of 3D interconnected periodic macroporous NaNbO3 (PM NaNbO3) to effectively increase the density of surface-active sites and optimize the photogenerated carrier-transfer efficiency. By incorporating Pt as a cocatalyst, PM NaNbO3 exhibits an exceptional photocatalytic hydrogen generation rate of 10.04 mmol h-1 g-1, which is approximately six and five times higher than those of calcined NaNbO3 (C-NaNbO3) and hydrothermal NaNbO3 (H-NaNbO3), respectively. This outstanding performance can be attributed to the synergistic effects arising from its well-interconnected pore architecture, large surface area, enhanced light absorption capability, and improved charge carrier separation and transport efficiency. The findings presented in this study demonstrate an innovative approach toward designing hierarchically periodic macroporous materials for solar-driven hydrogen production.

Long-lasting, fast-switchable photochromism in Na0.5Bi0.5TiO3 induced by photocatalytic memory effect, and its subsequently enhanced piezoelectric response and catalytic performances

A ferroelectric ceramic material of Na0.5Bi0.5TiO3 was found to possess a pronounced, long-lasting, and fast-switchable photochromic behavior responsive to visible light. The working mechanism of its photochromism could be attributed to an interesting photocatalytic memory effect, during which photogenerated electrons were trapped by Bi3+/Ti4+ and oxygen vacancies generated in Na0.5Bi0.5TiO3. The release kinetics of trapped electrons could be modulated by controlling environment conditions to make its photochromism phenomenon both long-lasting and fast-switchable to meet various application requirements. In the meantime, the photochromism process changed its inner electronic structure, resulting in stronger oxidation capability, increased piezoelectric response, improved charge carrier separation and transfer, and more active oxygen species production. Thus, its photocatalytic, piezocatalytic and photopiezocatalytic performances were all significantly enhanced as demonstrated by its TC-HCl degradation performances. This work offered a novel approach to search for and design inorganic photochromic materials with good reversibility for various technical applications.

Synergistic effect of Li, La co-doping on photocatalytic activity of BaTiO3 ferroelectric material for effective degradation of toxic NOx for environmental remediation

We investigated the synergistic effects of Li, La-doping and co-doping on the A-site of perovskite BaTiO3 microstructure as a catalyst for the removal of toxic NOx for environmental remediation. The Rietveld refinement of XRD and Raman analysis confirmed that at room temperature, the ceramic samples possessed a pure-tetragonal perovskite structure, with P4mm space group. SEM images revealed a denser microstructure with reduced grain size on Li, La doping in BaTiO3. XPS results confirmed the coexistence of Li and La as doping elements into BaTiO3 lattice. EPR and PL spectra demonstrate the presence of Ti and Ba vacancies as well as defects. According to the DRS results, the absorption edge of the co-doped sample was blue-shifted. In frequency-dependent dielectrics, the co-doped sample exhibits the greatest rise in dielectric permittivity. Impedance measurement demonstrates the fastest rate of charge transport in Ba0.98Li0.01La0.01TiO3. Similarly, Li and La incorporation into BaTiO3 significantly reduced the recombination extent of charge carriers as evidenced by the PL. Under UV light, the photocatalytic NOx degradation with Ba0.98Li0.01La0.01TiO3 achieved a remarkable 44 % efficiency during 60 min. This enhancement is associated with improved charge carrier separation at the interface between the ferroelectric surfaces. Only a marginal decrease in photocatalytic activity occurred after four consecutive runs. A reasonable photocatalytic mechanism for the degradation of NOx over Ba0.98Li0.01La0.01TiO3 is proposed. This study's findings can inspire the design and synthesis of rare earth and alkali metal ion co-doped photocatalysts with built-in electric fields of a ferroelectric material for efficient NOx removal from the environment.

Ligand Functionalization of Metal‐Organic Frameworks for Photocatalytic H2O2 Production

AbstractH2O2 production by photocatalysis has received considerable attention, while using MOF‐based materials as photocatalysts is still less explored. Ligand functionalization of MOFs is a decoration way at the molecular level, which provides the basis for the further modification of MOFs. In this concept, ligand functionalization of MOFs for photocatalytic H2O2 production has been systematically and extensively discussed. The strategies of ligand functionalization include grafting of functional groups (e. g. amino, methoxyl, boron and alkyl) and multiple ligand decoration. Correspondingly, some specific effects are achieved, e. g. improved charge carrier separation, enhanced O2 adsorption and hydrophobicity, which can realize efficient H2O2 production by photocatalysis. Meanwhile, reaction conditions and activities of photocatalytic H2O2 production have also been explicitly introduced in these studies. At last, the future perspectives are proposed. This concept sheds fresh light on the great potential of ligand functionalization of MOFs for photocatalytic H2O2 production.

Enhanced photocatalytic performance of Bi2MoO6 via strain engineering through collaborative optimization of indium doping and oxygen vacancies

Investigating lattice strain manipulation as an emerging strategy for improved photocatalysis, we introduce lattice strain into Bi2MoO6 nanosheets through synergistic indium doping and oxygen vacancies (OVs). Structural analysis reveals distinct compressive and tensile effects induced by indium doping and OVs, respectively, leading to localized lattice strain intensification. The optimized photocatalyst displays significantly enhanced tetracycline, ciprofloxacin, oxytetracycline, and norfloxacin removal activity due to increased active sites and improved charge carrier separation efficiency induced by lattice strain. Elucidation of tetracycline cleavage pathways and assessment of intermediate molecule toxicity are presented. This collaborative approach, merging doping and OVs for lattice strain induction, provides crucial insights for advancing bismuth-based photocatalysts.

WO3/FeOOH heterojunction for improved charge carrier separation and efficient photoelectrochemical water splitting

Photoanodes with sufficient visible light absorption, efficient photogenerated carrier separation and fast transport are still the main challenges for realizing high-efficiency photoelectrochemical (PEC) water splitting. Herein, we prepared the WO3/FeOOH heterojunction in situ grown on the FTO glass substrates by a facile seed-mediated two-step hydrothermal method. Under simulated sunlight irradiation, the prepared WO3/FeOOH heterojunction exhibits the enhanced photocurrent density of 2.63 mA cm−2 at 1.23 V vs. RHE, which is much higher than that of the bare WO3 film (1.62 mA cm−2 at 1.23 V vs. RHE). The excellent PEC performance of the sample can be attributed to the improved oxygen evolution kinetics and the extended visible light absorption range due to FeOOH, and the facilitation of carrier separation together with the suppressed recombination of photogenerated electron-hole pairs due to the formation of type-II WO3/FeOOH heterojunction. This work provides a promising approach for developing a highly efficient and cost-effective photoanode for application in solar-driven PEC water splitting.

Augmented photocatalysis induced by 1T-MoS2 bridged 2D/2D MgIn2S4@1T/2H-MoS2 Z-scheme heterojunction: mechanistic insights into H2O2 and H2 evolution.

In the realm of composite photocatalysts, the fusion of the co-catalyst effect with interfacial engineering is recognized as a potent strategy for facilitating the segregation and migration of photo-induced charge carriers. Herein, an innovative mediator-based Z-scheme hybrid, i.e. MIS@1T/2H-MoS2, has been well designed by pairing MIS with 1T/2H-MoS2via a facile hydrothermal strategy as a competent photocatalyst for H2O2 and H2 generation. The co-catalyst, i.e. metallic 1T-phase bridging between semiconducting 2H-MoS2 and MIS, serves as a solid state electron mediator in the heterostructure. Morphological findings revealed the growth of 1T/2H-MoS2 nanoflowers over MIS microflowers, verifying the close interaction between MIS and 1T/2H-MoS2. By virtue of accelerated e-/h+ pair separation and migration efficiency along with a proliferated density of active sites, the MMoS2-30 photocatalyst yields an optimum H2O2 of 35 μmol h-1 and H2 of 370 μmol h-1 (ACE of 5.9%), which is 3 and 2.7 fold higher than pristine MIS. This obvious enhancement can be attributed to photoluminescence and electrochemical aspects that substantiate the diminished charge transfer resistance along with improved charge carrier separation, representing a good example of a noble metal-free photocatalyst. The proposed Z-scheme charge transfer mechanism is aided by time-resolved photoluminescence (TRPL), XPS, radical trapping experiments, and EPR analysis. Overall, this endeavour provides advanced insights into the architecture of noble metal-free Z-scheme heterostructures, offering promising prospects in photocatalytic applications.

Fabrication of high-surface-area mesoporous frameworks of β-Ni(OH)2–CdIn2S4 p–n nano-heterojunctions for improved visible light photocatalytic hydrogen production

High-surface-area mesoporous frameworks of Ni-decorated CdIn2S4 nanocrystals offer prominent advantages for light-induced catalysis due to the large surface area and improved charge carrier separation kinetics at the p–n β-Ni(OH)2/CdIn2S4 junctions.

Insights into the photocatalytic role of glycine-assisted sol-gel auto-combustion synthesized (Co, Mn)(Co, Mn)2O4 nanostructures for efficient visible light-driven degradation of methyl orange

Research on the use of new materials and the improvement of existing fast ways for removal of water pollutants is still challenging. This work documented rational fabrication of (Co, Mn)(Co, Mn)2O4 nanoparticles as nano-photocatalyst materials with improved charge carrier separation and strong redox potential for efficient degradation of methyl orange (MO) in wastewater. This investigation illustrated that the Co/Mn molar ratio can greatly affect the textural and structural properties. From the point of view of size and shape, the optimum product with 1:3 M ratio of Co to Mn precursors was selected as a catalyst in the photocatalysis process. The prepared highly crystallized phase of tetragonal (Co, Mn)(Co, Mn)2O4 describe an optical band gap of 1.7 eV, according to the DRS data, which make them as efficient visible driven photocatalysts. The photodegradation experiments of spinel mixed structures were assessed by investigation of photocatalyst dosages and initial MO concentrations to unravel how these operational parameters affect Co-Mn-O photocatalysis. A remarkable discoloration capability of 68.07 % could result from the catalyst dosage of 0.04 g and dye concentration of 15 mg/L after 120 min of visible light. The kinetics survey further unveiled the maximum rate constant of 0.0080 min−1 for the MO degradation. In the scavenger trials, singlet oxygen (1O2) and superoxide (●O2−) radicals were principal reactive oxygen species (ROS) responsible for pollutant photodegradation in the presence of pure (Co, Mn)(Co, Mn)2O4 structures. In addition, the cyclic performance of catalyst depicted a removal efficiency of 60.1 % over 5 runs.

Photocatalytic Activity and Electron Storage Capability of TiO2 Aerogels with Adjustable Surface Area

Nanostructuring of semiconductor photocatalysts is one important strategy to improve photocatalytic activities. An interesting nanostructuring strategy is the generation of mesoporosity, i.e. in aerogels. Aerogels are 3D nanostructures of interconnected porous networks with enormous porosity, ultra-low density, and high surface areas, which are higher than surface areas of particle systems.[1,2] The high surface area and presumably high amount of reactive sites and a good contact of the active material to the electrolyte, as well as short diffusion pathways for the minority charge carriers and an improved charge carrier separation are advantageous for photocatalytic applications.[3-5]TiO2 aerogels offer a higher density of photoexcited electrons compared to TiO2 nanoparticles.[5] Electrons in TiO2 are trapped close to the surface of the material and Ti3+ states are formed, which show a characteristic dark blue coloration, i.e. a broad absorption at a maximum of 650 nm.[6-8] Stored photoexcited electrons in TiO2 can be used for different dark reduction reactions.[7-10] A very promising reduction reaction using such stored photoexcited electrons is the nitrogen reduction reaction for the production of ammonia, which was first reported by Bahnemann et al. in 2011 for stored electrons in TiO2.[8] This reaction can pave the way to an energy efficient and decentralized production of ammonia, which is commonly produced via the extremely energy intensive Haber-Bosch process, which causes 2 % of the annual global energy consumption and 1.6 % of the global CO2 emissions.[11]Herein, we present the photocatalytic hydrogen evolution activity and electron storage capability of mesoporous TiO2 aerogels which were prepared via a novel acid-catalyzed sol-gel synthesis with subsequent supercritical drying.[12] The as-synthesized aerogel provided a surface area of 600 m2 g-1 which could be tailored by different heat treatments. The sacrificial hydrogen evolution activity of the aerogels decreased with increasing surface area and decreasing crystallinity. At the same time, the addition of an aqueous H2PtCl6 solution to the bluish dispersions in the dark resulted in the evolution of hydrogen without light irradiation, due to the reduction of Pt4+ to Pt0 and the formation of a Schottky contact. The intensity of that dark hydrogen evolution peak increased with increasing surface area. This reduction reaction could be used to quantify the amount of electrons stored in the aerogels. Furthermore, it could be shown that the electron storage capability depends on the hole acceptor concentration. The ability to reduce nitrogen to ammonia in the dark with the stored photoexcited electrons in such an aerogel will be presented. These results pave the way for future research on the optimization of aerogel properties depending on their future application together with optimization of photocatalytic nitrogen reduction and other reduction reactions with such aerogels.[1] S. Alwin et al. Mater. Renew. Sustain. Energy 2020, 9, 7[2] N. Hüsing et al. Angew. Chemie Int. Ed. 1998, 37, 22[3] M. L. Anderson et al. Adv. Eng. Mater. 2000, 2, 481[4] P. A. DeSario et al. J. Phys. Chem. C 2015, 119, 17529[5] D. A. Panayotov et al. J. Phys. Chem. C 2013, 117, 15035[6] D. Bahnemann et al. J. Phys. Chem. 1984, 88, 709[7] H. H. Mohamed et al. J. Phys. Chem. A 2011, 115, 2139[8] H. H. Mohamed et al. Chem. - A Eur. J. 2012, 18, 4314[9] H. H. Mohamed et al. J. Photochem. Photobiol. A Chem. 2011, 217, 271[10] H. H. Mohamed et al. J. Photochem. Photobiol. A Chem. 2012, 245, 9[11] K. Wang et al. Carbon Resour. Convers. 2018, 1, 2[12] A. Rose et al. ACS Appl. Energy Mater. 2022, 5, 14966

Exceptional piezocatalytic H2 production of nitrogen-doped TiO2@carbon nanosheets induced by engineered piezoelectricity

Piezocatalytic hydrogen evolution is a promising strategy to generate sustainable energy. In this report, nitrogen-doped (N-doped) TiO2@ carbon nanosheets (N-TiO2@C NSs) was successfully synthesized using C3N4 as a multifunctional template. During the synthesis, the two-dimensional (2D) architecture of C3N4 nanosheets directed the synthesis of TiO2 nanosheets. In addition, nitrogens of C3N4 were doped into the TiO2 lattice. Simultaneously, C3N4 was transformed into N-doped carbon nanosheets. N doping broke the crystal symmetry of TiO2, which endowed TiO2 with promising piezoelectric properties. The N-doped carbon nanosheets derived from C3N4 improved charge carrier separation efficiency and served as a flexible support to inhibit structural damage under sonication. Therefore, the N-TiO2@C NSs exhibited highly efficient activity for piezocatalytic H2 production (6.4 mmol·g−1·h−1) in the presence of methanol, much higher than those of the previously reported piezocatalysts. Our method is hoped to provide a new strategy for designing highly efficient piezocatalysts.