Enhanced tribocatalytic degradation performance of organic pollutants by Cu1.8S/CuCo2S4 p-n junction

Tribocatalysis research, leveraging the triboelectric effect, presents significant potential for environmental water pollution control. However, there is a notable scarcity of studies pertaining to tribocatalysis involving heterojunctions, particularly in the context of p-n junction tribocatalysis. In this study, we employed a one-step solvothermal method to synthesize a Cu1.8S/CuCo2S4 p-n junction composite catalyst. Subsequently, we explored the tribocatalytic degradation performance of organic pollutants facilitated by the Cu1.8S/CuCo2S4 catalyst. The findings reveal that, under simple magnetic stirring conditions, the degradation rates achieved by the Cu1.8S/CuCo2S4 catalyst for tetracycline (TC), methylene blue (MB), and methyl orange (MO) are remarkably high, reaching 99.9 %, 99.7 %, and 94.0 %, respectively. This underscores the broad applicability of the Cu1.8S/CuCo2S4 catalyst for the tribocatalytic degradation of diverse organic pollutants. Experimental evidence establishes that friction occurring between the polytetrafluoroethylene (PTFE) magnet rod, the beaker, and the catalyst induces charge transfer at their interfaces, generating highly oxidized active species that effectively decompose pollutants. Through free radical capture and electron spin resonance (ESR) tests, it was empirically determined and validated that the principal active species involved in tribocatalytic degradation are holes (h+) and superoxide radicals (O2-). Incorporating insights from the experimental characterization of p-n junctions and density functional theory (DFT) theoretical calculations, we propose a plausible tribocatalytic mechanism for Cu1.8S/CuCo2S4. This research not only contributes novel findings but also serves as a reference for the exploration of innovative heterojunction tribocatalysts.

Enhanced electrocatalytic efficiencies for water electrolysis and para-nitrophenol hydrogenation by self-supported nickel cobalt phosphide-nickel iron layered double hydroxide p-n junction

Charge redistribution across heterointerfaces is an important tactic to enhance the catalytic activities and bifunctionality of hybrid catalysts, especially for green hydrogen production from water electrolysis and harmless electrocatalytic valorization of organics. Herein, a self-supported p-n junction catalytic electrode was constructed by tandem electrodeposition of nickel cobalt phosphide (NiCoP) and nickel iron layered double hydroxide (NiFe LDH) onto Ni foam (NF) substrate, denoted as NiCoP@NiFe LDH/NF, to enhance the electrocatalytic capabilities for water electrolysis and hydrogenation of an organic, para-nitrophenol (4-NP). Benefitting from the charge redistribution across the p-n junction, high electrocatalytic efficiencies for oxygen evolution reaction (OER, overpotential of 388 mV at 100 mA cm-2) and hydrogen evolution reaction (HER, overpotential of 132 mV at 10 mA cm-2) could be achieved concurrently by the NiCoP@NiFe LDH/NF electrode, and both overpotentials were located within the mainstream levels in this domain. The bifunctional catalytic features enabled a full water electrolysis response of 10 mA cm-2 at 1.61 V. In addition, the p-n junction electrode catalyzed the hydrogenation of 4-NP at a conversion of 100%, para-aminophenol (4-AP) selectivity of 90% and faradaic efficiency (FE) of 88% at -0.18 V. The current work offers a feasible strategy for fulfilling electrochemical H2 production and hydrogenation valorization of 4-NP pollutant by constructing a self-supported p-n junction catalytic electrode.

Boosting photocatalytic synchronous production of H2 coupled with acetone over Co doped Cu3P quantum dots/ZnIn2S4 nanosheets p-n nanojunction

Photocatalysis provides a new way for synchronous H₂ production and organic synthesis at normal temperature and pressure, usually, water and organic substrate function as sources of hydrogen protons and organic products, which are complex and limited by two half-reactions. Employing alcohols as reaction substrates to simultaneously produce H₂ and valuable organics in a redox cycle is worthy studying, to which catalyst design at atomic level holds the key. In this paper, Co elements doped Cu₃P (CoCuP) quantum dots (QDs) are prepared and coupled with ZnIn₂S₄ (ZIS) nanosheets to form a 0D/2D p-n nanojunction which can effectively boost aliphatic and aromatic alcohols activation to simultaneously produce H₂ and corresponding ketones (or aldehydes). The optimal CoCuP/ZIS composite demonstrated the highest activity for dehydrogenation of isopropanol to acetone (17.77 mmol⋅g^-1⋅h^-1) and H₂ (26.8 mmol⋅g^-1⋅h^-1), which was 2.40 and 1.63 times higher than that of Cu₃P/ZIS composite, respectively. Mechanistic investigations revealed that such high-performance originated from the accelerated electron transfer of the formed p-n junction and the thermodynamic optimization caused by the Co dopant which was the active site of oxydehydrogenation as a prerequisite step for isopropanol oxidation over the surface of the CoCuP/ZIS composite. Besides that, coupling of the CoCuP QDs can lower the dehydrogenation activation energy of isopropanol to form a key radical intermediate of (CH₃)₂CHO* for improving the activity of simultaneous production of H₂ and acetone. This strategy provides an overall reaction strategy to obtain two meaningful products (H₂ and ketones (or aldehydes)) and deeply explores the integrated redox reaction of alcohol as substrate for high solar-chemical energy conversion.

Sulfur vacancy and p-n junction synergistically boosting interfacial charge transfer and separation in ZnIn2S4/NiWO4 heterostructure for enhanced photocatalytic hydrogen evolution

Constructing a p-n heterojunction with vacancy is advantageous for speeding up carrier separation and migration due to the synergy of the built-in electric field and electron capture of the vacancy. Herein, a sulfur vacancy riched-ZnIn₂S₄/NiWO₄ p-n heterojunction (VZIS/NWO) photocatalyst was rationally designed and fabricated for photocatalytic hydrogen evolution. The composition and structure of VZIS/NWO were characterized. The existence of sulfur vacancy was confirmed through X-ray photoelectron spectroscopy, high-resolution transmission electron microscope, and electron paramagnetic resonance technology. The p-n heterojunction formed by ZnIn₂S₄ and NiWO₄ was proved to provide a convenient channel to boost interfacial charge migration and separation. By reducing the band gap, the vacancy engineer can improve light absorption as well as serve as an electron trap to improve photo-induced electron-hole separation. Benefiting from the synergy of p-n heterojunction and vacancy, the optimal VZIS/NWO-5 catalyst exhibits dramatically enhanced H₂ generation performance, which is about 10-fold that of the pristine ZnIn₂S₄. This work emphasizes the synergy between p-n heterojunction and sulfur vacancy for enhancing photocatalytic hydrogen evolution performance.

Integrated p-n/Schottky junctions for efficient photocatalytic hydrogen evolution upon Cu@TiO2-Cu2O ternary hybrids with steering charge transfer

Solar-driven photocatalytic H₂ evolution could tackle the issue of fossil fuels-triggered greenhouse gas emission with sustainable clean energy. However, splitting water into hydrogen with high performance by a single semiconductor is challenging because of the poor charge separation efficiency. Herein, a novel ternary Cu@TiO₂-Cu₂O hybrid photocatalyst with multiple charge transfer channels has been designed for efficient solar-to-hydrogen evolution. Indeed, the ternary Cu@TiO₂-Cu₂O hybrid by coupling Cu@TiO₂ with Cu₂O nanoparticles shows highly-efficient photocatalytic hydrogen generation with rate of 12000.6 μmol·g^-1·h^-1, which is 4.4, 2.1, and 1.9 times higher than the pure TiO₂ (2728.8 μmol·g^-1·h^-1), binary Cu@TiO₂ (5595.5 μmol·g^-1·h^-1), and TiO₂-Cu₂O (6076.8 μmol·g^-1·h^-1) composite, respectively. In such a Cu@TiO₂-Cu₂O hybrid, the formed internal electric field in the TiO₂-Cu₂O p-n junction allows the electrons in Cu₂O to migrate to TiO₂, while the electrons in the CB of TiO₂ could flow into Cu via the Schottky junction at the Cu@TiO₂ interface. In this regard, a multiple charge transfer is achieved between the Cu@TiO₂ and Cu₂O, which facilitates promoted charge separation and results in the construction of electron-accumulated center (Cu) and hole-enriched surface (Cu₂O). This p-n/Schottky junctions with steered charge transfer assists the hydrogen production upon the Cu@TiO₂-Cu₂O ternary photocatalyst.

Uniform H-CdS@NiCoP core-shell nanosphere for highly efficient visible-light-driven photocatalytic H2 evolution

Constructing highly efficient and cost-effective photocatalyst system has been a big challenge for photocatalysis. Herein, CdS nanosphere (N-CdS), hollow CdS (H-CdS) and a series of H-CdS@NiCoP core-shell nanospheres have been successfully prepared via a facile hydrothermal method. The activity test showed that H-CdS exhibited higher photocatalytic activity (3.34 mmol g^-1h^-1) compared with N-CdS (0.99 mmol g^-1h^-1) under visible light irradiation (λ ≥ 420 nm), suggesting that hollow structure could effectively improve photocatalytic activity. Moreover, the H-CdS@NiCoP-7 wt% displayed a maximum photocatalytic H₂ evolution rate of 13.47 mmol g^-1h^-1, which was about 4 times and 2.5 times higher than that of pristine H-CdS and H-CdS@Pt-3 wt%, respectively. Furthermore, H-CdS@NiCoP-7 wt% exhibited a good stability during 20 h test. The physicochemical properties were characterized by XRD, SEM, TEM, XPS, UV-vis DRS, PL and photoelectrochemical technique. The results showed that NiCoP addition can construct p-n junction with H-CdS and effectively promote the charge transfer from CdS to NiCoP, which improved the photocatalytic hydrogen evolution activity. This work revealed that NiCoP could react as an excellent co-catalyst for enhancing H-CdS photocatalytic activity.

Hydrogen spillover effect induced by ascorbic acid in CdS/NiO core-shell p-n heterojunction for significantly enhanced photocatalytic H2 evolution

A new variety of CdS/NiO core-shell p-n heterojunction is synthesized by in-situ chemically depositing NiO shell on single-crystal CdS nanorods for the first time. With this method, the range of NiO shell thickness can be accurately controlled within a few nanometers. The optimized CdS/NiO sample (CSN_0.5) with a NiO shell layer of 1.5 nm exhibits a highly efficient photocatalytic H₂ evolution rate of 731.7 μmol/h (corresponding to 243.9 mmol/g/h) without using co-catalyst, which is among the highest value of all the CdS-based photocatalysts. The apparent quantum efficiency (AQE) of CSN_0.5 at 365 nm wavelength reaches 28.19%. The remarkably enhanced photocatalytic performance can be attributed to a hydrogen spillover effect induced by ascorbic acid in CdS/NiO, which promotes the transmission of adsorbed H* from hydrogen-rich NiO (electron-poor region) to hydrogen-poor CdS (electron-rich region) where the adsorbed H* reacts in time with the photogenerated electron to produce H₂, facilitating the H₂ evolution reaction. This work provides a method to promote the photocatalytic H₂ evolution reaction by using hydrogen spillover effect.

Enhanced faradic activity by construction of p-n junction within reduced graphene oxide@cobalt nickel sulfide@nickle cobalt layered double hydroxide composite electrode for charge storage in hybrid supercapacitor

The intrinsic faradic reactivity is the uppermost factor determining the charge storage capability of battery material, the construction of p-n junction composing of different faradic components is a rational tactics to enhance the faradic activity. Herein, a reduced graphene oxide@cobalt nickle sulfide@nickle cobalt layered double hydroxide composite (rGO@CoNi₂S₄@NiCo LDH) with p-n junction structure is designed by deposition of n-type nickle cobalt layered double hydroxide (NiCo LDH) around p-type reduced graphene oxide@cobalt nickle sulfide (rGO@CoNi₂S₄), the charge redistribution across the p-n junction enables enhanced faradic activities of both components and further the overall charge storage capacity of the resultant rGO@CoNi₂S₄@NiCo LDH battery electrode. As expected, the rGO@CoNi₂S₄@NiCo LDH electrode can deliver high specific capacity (C_s, 1310 ± 26 C g^-1 at 1 A g^-1) and good cycleability (77% C_s maintaining ratio undergoes 5000 charge-discharge cycles). Furthermore, the hybrid supercapacitor (HSC) based on the rGO@CoNi₂S₄@NiCo LDH p-n junction battery electrode exports high energy density (E_cell, 57.4 Wh kg^-1 at 323 W kg^-1) and good durability, showing the prospect of faradic p-n junction composite in battery typed energy storage.

Light enhanced room temperature resistive NO2 sensor based on a gold-loaded organic-inorganic hybrid perovskite incorporating tin dioxide

A material is described for sensing NO₂ in the gas phase. It has an architecture of type Au/MASnI₃/SnO₂ (where MA stands for methylammonium cation) and was fabricated by first synthesizing Au/MASnI₃ and then crystallizing SnO₂ on the surface by calcination. The physical and NO₂ sensing properties of the composite were examined at room temperature without and with UV (365 nm) illumination, and the NO₂-sensing mechanism was studied. The characterization demonstrated the formation of a p-n heterojunction structure between p-MASnI₃ and n-SnO₂. The sensor, best operated at a voltage of 1.1 V at room temperature, displays superior NO₂ sensing performance. Figures of merit include (a) high response (R_g/R_a = 240 for 5 ppm NO₂; where R_g stands for the resistance of a sensor in test gas, and R_a stands for the resistance of a sensor in air), (b) fast recovery (about 12 s), (c) excellent selectivity compared to sensors based on the use of SnO₂ or Au/SnO₂ only, both at room temperature under UV illumination; (d) a low detection limit (55 ppb), and (e) a linear response between 0.5 and 10 ppm of NO₂. The enhanced sensing performance is mainly attributed to the high light absorption capacity of MASnI₃, the easy generation and transfer of photo-induced electrons from MASnI₃ to the conduction band of SnO₂, and the catalytic effect of gold nanoparticles. Graphical abstract Schematic of the energy band diagrams of the gold-functionalized MASnI₃/SnO₂ system after equilibrium with UV illumination, by which the enhanced sensing performance for NO₂ can be explained.

Photocatalytic Properties of Co3O4-Coated TiO2 Powders Prepared by Plasma-Enhanced Atomic Layer Deposition

Co₃O₄-coated commercial TiO₂ powders (P25) p-n junction photocatalysts were prepared by plasma-enhanced atomic layer deposition (PEALD) technique. The structure, morphology, bandgap, and photocatalytic properties under ultraviolet light were investigated systematically. Although the deposition of Co₃O₄ does not change the anatase structure and crystallite size of P25 powders, the ultraviolet photocatalytic activity has been improved evidently. For the Co₃O₄-coated P25 powders, the trace Co ions exist as Co₃O₄ nanoparticles attached to TiO₂ powder surface instead of the occupation of Ti⁴⁺ position in TiO₂ lattice. The Co₃O₄-coated P25 powders exhibit enhanced photocatalytic degradation efficiency of almost 100% for methylene blue in 1.5 h under ultraviolet light, compared with P25 of 80%. The Mott-Schottky plots of photocatalyst powders confirm the p-n heterojunction formation in Co₃O₄-TiO₂ nanocomposite materials, which is beneficial to increase the efficiency of photogenerated electron-hole separation. In addition, the Co₃O₄ coating also promotes the adsorption of organic dyes of methylene blue on P25 powders.

Structural and electrical properties of oxygen complexes in Cz and FZ silicon crystals implanted with carbon ions

We present a comparative study of thermal donor (TD) center formation mechanisms as a result of carbon ion implantation into float zone (FZ-Si) and Czochralski (Cz-Si) silicon crystals. The kinetics of the TD center formation and transformation of their structure during annealing have been investigated. Also, the TD center formation takes place after additional oxygen implantation into FZ/Cz-Si, and an important role of recoil oxygen atoms (from the screen oxide) has been demonstrated for the FZ-Si case. Their concentration in the Si surface layer depends on the implantation dose and the screen oxide thickness, reaching up to values 10(18) to 10(19) cm(-3), which is comparable with the oxygen concentration in Cz-Si. These oxygen atoms can lead to additional thermal donor centers generation, especially in the FZ-Si.

PACS

34.50.Dy; 61.10.-i; 68.35.Dv.