Approach of fermi level and electron-trap level in cadmium sulfide nanorods via molybdenum doping with enhanced carrier separation for boosted photocatalytic hydrogen production

Vacancy Engineering in 2D Transition Metal Chalcogenide Photocatalyst: Structure Modulation, Function and Synergy Application

Transition metal chalcogenides (TMCs) are widely used in photocatalytic fields such as hydrogen evolution, nitrogen fixation, and pollutant degradation due to their suitable bandgaps, tunable electronic and optical properties, and strong reducing ability. The unique 2D malleability structure provides a pre-designed platform for customizable structures. The introduction of vacancy engineering makes up for the shortcomings of photocorrosion and limited light response and provides the greatest support for TMCs in terms of kinetics and thermodynamics in photocatalysis. This work reviews the effect of vacancy engineering on photocatalytic performance based on 2D semiconductor TMCs. The characteristics of vacancy introduction strategies are summarized, and the development of photocatalysis of vacancy engineering TMCs materials in energy conversion, degradation, and biological applications is reviewed. The contribution of vacancies in the optical range and charge transfer kinetics is also discussed from the perspective of structure manipulation. Vacancy engineering not only controls and optimizes the structure of the TMCs, but also improves the optical properties, charge transfer, and surface properties. The synergies between TMCs vacancy engineering and atomic doping, other vacancies, and heterojunction composite techniques are discussed in detail, followed by a summary of current trends and potential for expansion.

CdS/ZnS core-shell nanorod heterostructures co-deposited with ultrathin MoS2 cocatalyst for competent hydrogen evolution under visible-light irradiation

Hydrogen generation via semiconductor photocatalysts has gained significant attention as a sustainable fuel generation process. To demonstrate the performance of nanoscale core-shell heterostructure in photocatalytic hydrogen production, we have fabricated CdS nanorods coated with ZnS photocatalyst via wet-chemical reaction followed by deposition of ultrathin MoS2 nanosheets by photo reduction process. The effect of ZnS content and suitable amount of MoS2 loading over the visible-light induced photocatalytic hydrogen evolution was examined in Na2S and Na2SO3 aqueous solutions. Interestingly, it is apparent that a close connection (or heterojunction) between CdS and ZnS is believed to easily tunnel the charge carriers to the surplus surface states, making its electrons and holes energetically favourable to transfer from ZnS to MoS2 for photocatalytic reactions and subsequently, enhances the H2 evolution activity in CdS/ZnS type I core-shell heterostructures. The optimal MoS2 concentration is resolved to be 7 mol% and the subsequent visible-light induced H2 generation rate was 13589 μmol h-1g-1, which is 19 and 158 fold higher than pristine CdS and ZnS respectively. The probable photocatalytic mechanism of CdS/ZnS type I core-shell heterostructure with MoS2 cocatalyst is proposed. Our inexpensive and convenient preparation strategy may offer novel prospects in the engineering of desirable nanoheterostructures with better performance.

Theory guided engineering of zeolite adsorbents for acaricide residue adsorption from the environment

CONTEXT

Zeolites have attracted attention for their potential in adsorbing environmental contaminants. However, contaminants, such as acaricides used extensively in livestock production to control ticks and mites, have received limited exploration regarding their adsorption onto zeolite surfaces. This study aimed to identify the most appropriate zeolite frameworks for the adsorption of acaricide residues, deduce the mechanism underlying the adsorption process, and evaluate the impact of surface modification on the adsorption capabilities of zeolites.

METHODS

Grand Canonical Monte Carlo (GCMC) was used to screen the entire zeolite database to analyze their adsorption properties, where the cloverite zeolite framework (CLO) exhibits the highest adsorption capacity (percentage weight, 54%). Machine learning was employed to rank structural feature importance on adsorption. Density and helium void fraction appeared to be the most important structural features. Thus, engineering these features is of utmost significance in harvesting the desired acaricides. The second step involved engineering the structural and electronic properties of the shortlisted zeolite frameworks via cation substitution with suitable atoms. DFT calculations involving natural bond orbital (NBO) analysis and quantum theory of atoms in molecules (QTAIM) have been done to understand the influence of cation substitution on the electronic structure.

Dual-defect semiconductor photocatalysts for solar-to-chemical conversion: advances and challenges

Among the renewable energy technologies to deal with increasing energy crisis and environmental concerns, solar-to-chemical conversion via photocatalysis holds great promise for sustainable energy supply. To date, a variety of modification strategies with different types of semiconducting materials have been proposed to boost photocatalytic efficiency. Recently, dual-defect semiconductor photocatalysts have emerged as an advantageous candidate with superior performance in improving photocatalytic activity compared to their defect-free or single-defect counterparts. In this review, focus is laid on the advances of dual-defect semiconductor photocatalysts for energy photocatalysis. Possible schemes for two different defects within a single semiconductor are firstly sorted based on the types of defects, and synthesis strategies to achieve various defect schemes as well as techniques to characterize different defects are then introduced. In particular, the effect of different defects on photocatalytic performance is emphasized, and the advances in dual-defect semiconductors for solar-to-chemical conversions are summarized based on different defect schemes. Finally, the future challenges and opportunities of dual-defect semiconductors for photocatalysis are discussed. This article is expected to provide an overall insight into existing dual-defect semiconductor photocatalysts and inspire the development of new defect-rich materials for photocatalytic energy production.

Tuning the morphology, stability and optical properties of CsSnBr3 nanocrystals through bismuth doping for visible-light-driven applications

In this investigation, we have demonstrated the synthesis of lead-free CsSnBr3 (CSB) and 5 mol% bismuth (Bi) doped CSB (CSB'B) nanocrystals, with a stable cubic perovskite structure following a facile hot injection technique. The Bi substitution in CSB was found to play a vital role in reducing the size of the nanocrystals significantly, from 316 ± 93 to 87 ± 22 nm. Additionally, Bi doping has inhibited the oxidation of Sn2+ of CSB perovskite. A reduction in the optical band gap from 1.89 to 1.73 eV was observed for CSB'B and the PL intensity was quenched due to the introduction of the Bi3+ dopant. To demonstrate one of the visible-light-driven applications of the nanocrystals, photodegradation experiments were carried out as a test case. Interestingly, under UV-vis irradiation, the degradation efficiency of CSB'B was roughly one order lower than that of P25 titania nanoparticles; however, it was almost five times higher when driven by visible light under identical conditions. The water stability of CSB'B perovskite and suppression of the oxidative degradation of Sn were confirmed through XRD and XPS analyses after photocatalysis. Moreover, by employing experimental parameters, DFT-based first-principles calculations were performed, which demonstrated an excellent qualitative agreement between experimental and theoretical outcomes. The as-synthesized Bi-doped CSB might be a stable halide perovskite with potential in visible-light-driven applications.

MoS2-Based Nanocomposites for Photocatalytic Hydrogen Evolution and Carbon Dioxide Reduction

Photocatalysis is a facile and sustainable approach for energy conversion and environmental remediation by generating solar fuels from water splitting. Due to their two-dimensional (2D) layered structure and excellent physicochemical properties, molybdenum disulfide (MoS₂) has been effectively utilized in photocatalytic H₂ evolution reaction (HER) and CO₂ reduction. The photocatalytic efficiency of MoS₂ greatly depends on the active edge sites present in their layered structure. Modifications like reducing the layer numbers, creating defective structures, and adopting different morphologies produce more unsaturated S atoms as active edge sites. Hence, MoS₂ acts as a cocatalyst in nanocomposites/heterojunctions to facilitate the photogenerated electron transfer. This review highlights the role of MoS₂ as a cocatalyst for nanocomposites in H₂ evolution reaction and CO₂ reduction. The H₂ evolution activity has been described comprehensively as binary (with metal oxide, carbonaceous materials, metal sulfides, and metal-organic frameworks) and ternary composites of MoS₂. Photocatalytic CO₂ reduction is a more complex and challenging process that demands an efficient light-responsive semiconductor catalyst to tackle the thermodynamic and kinetic factors. Photocatalytic reduction of CO₂ using MoS₂ is an emerging topic and would be a cost-effective substitute for noble catalysts. Herein, we also exclusively envisioned the possibility of layered MoS₂ and its composites in this area. This review is expected to furnish an understanding of the diverse roles of MoS₂ in solar fuel generation, thus endorsing an interest in utilizing this unique layered structure to create nanostructures for future energy applications.

Ni-Doped In2O3 Nanoparticles and Their Composite with rGO for Efficient Degradation of Organic Pollutants in Wastewater under Visible Light Irradiation

The efficient degradation of organic effluent is always desirable when using advanced photocatalysts with enhanced activity under visible light. Nickel-doped indium oxide (Ni-In₂O₃) is synthesized via a hydrothermal route as well as its composites with reduced graphene oxide (rGO). Facile synthesis and composite formation methods lead to a well-defined morphology of fabricated nanocomposite at low temperatures. The bandgap energy of indium oxide lies in the range of 3.00-4.30 eV. Its high light absorption capacity, high stability, and non-toxicity make it a choice as a photocatalyst that is active under visible light. The transition metal Ni-doping changes the indium oxide's chemical, optical, and physicochemical properties. The Ni-In₂O₃ and rGO composites improved the charge transport and reduced the charge recombination. The phase analysis of the developed photocatalysts was performed using X-ray diffraction (XRD), and the morphological and structural properties were observed using advanced microscopic techniques (SEM and TEM), while UV-vis and FTIR spectroscopic techniques were used to confirm the structure and optical and chemical properties. The electrochemical properties of the photocatalysts were investigated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS), and the charge-transfer properties of the obtained photocatalysts and the mechanism of the photocatalytic degradation mechanism of methylene blue, a common dye used in the dyeing industry, were determined.

Synthesis and characterisation of Ga- and In-doped CdS by solventless thermolysis of single source precursors

We report a facile and low temperature synthesis of Ga- and In-doped CdS nanoparticles from molecular precursors. Diethyldithiocarbamate complexes of Cd(II), Ga(III), and In(III), were synthesised and decomposed in tandem through solventless thermolysis, producing Ga- or In-doped CdS. The resultant M_xCd_1-xS_1+0.5x (where M = Ga/In at x values of 0, 0.02, 0.04, 0.06, 0.08 and 0.1) particulate powder was analysed by powder X-ray diffraction, which showed that both Ga (through all doping levels) and In (at doping levels <8 mol%) were successfully incorporated into the hexagonal CdS lattice without any impurities. Raman spectroscopy also showed no significant change from CdS. Scanning electron microscopy and energy dispersive X-ray spectroscopy were used to investigate the morphology and elemental dispersion through the doped CdS materials, showing homogenous incorporation of dopant. The optical and luminescent properties of the doped M_xCd_1-xS_1+0.5x materials were examined by UV-Vis absorption and photoluminescence spectroscopies respectively. All materials were found to exhibit excitonic emission, corresponding to band gap energies between 2.7 and 2.9 eV and surface defect induced emission which is more prominent for Ga than for In doping. Additionally, moderate doping slows down charge carrier recombination by increasing the lifetimes of excitonic and surface state emissions, but particularly for the latter process.

One-pot solvothermal synthesis of flower-like Fe-doped In2S3/Fe3S4 S-scheme hetero-microspheres with enhanced interfacial electric field and boosted visible-light-driven CO2 reduction

S-scheme heterojunctions hold great potential for CO2 photoreduction into solar fuels, but their activities are severely limited by the low efficiency of interfacial charge transfer. In this work, a facile one-pot solvothermal reaction has been developed to dope Fe into flower-like In2S3/Fe3S4 hetero-microspheres (Fe-In2S3/Fe3S4 HMSs), which are demonstrated as an efficient S-scheme photocatalyst for visible-light-driven CO2 photoreduction. The doping of Fe not only reduces the bandgap of In2S3 and thus extends the optical response to the visible-light region, but also increases the densities of donors and sulfur vacancies, which leads to an elevated Fermi level (Ef). The difference of Ef between In2S3 and Fe3S4 is enlarged and their band bending at the interface is therefore enhanced, which results in promoted carriers transfer in the S-scheme pathway due to the reinforced interfacial electric field. Moreover, Fe-doped In2S3 reduces the formation energy of the *CO intermediate, which thermodynamically favors the CO evolution at the surface. As a result, the Fe-In2S3/Fe3S4 HMSs exhibit a significantly boosted CO2 photoreduction activity in comparison with bare In2S3 and Fe-In2S3 samples. This work demonstrates the great potential of heteroatom-engineered S-scheme photocatalysts for CO2 photoreduction.

Effect of Nitrogen Doping in GO as Support in ZnO/GO-N Compounds and Their Photocatalytic Assessment to Degrade the Lignin Molecule

Control of the recombination process and improvement of transport charge carriers could be achieved in photocatalysts by modifying the catalytic support. In the present study, our goal was to study the effect of nitrogen doping on graphene oxide sheets using doping sources such as urea, thiourea, or ethylenediamine to produce GO-N catalytic supports which were used to form ZnO/GO-N systems. The synthesis of ZnO and GO-N was carried out through a hydrothermal process under microwave heating. The ZnO/GO-N compounds were tested to study the degradation of the lignin molecule under UV irradiation. A set of characterization techniques were used to study the ZnO/GO-N compounds, including XPS analyses which confirmed the N-doping in the samples. The ZnO compound reached 40% of lignin degradation in 70 min, while the ZnO/GO-N compound produced 79% of lignin degradation, also in 70 min evidencing the positive effect of the GO-N support. The best results of degradation were obtained when thiourea was used as the N-doping media.

A Laser-Induced Photoelectrochemical Sensor for Natural Sweat Cu2+ Detection

Tracking fluctuations in the Cu2+ level in sweat is meaningful for non-invasive and real-time assessment of Cu2+-abnormality-related diseases and provides important diagnostic information. However, the user-unfriendly ways to obtain sweat and sweat biofouling have limited the development of this field. Herein, we exploit a highly sensitive photoelectrochemical (PEC) sensor as a detection method, a powerful laser engraving technique for the large-scale fabrication of laser-induced graphene and In-doped CdS (LIG-In-CdS) photoelectrodes, and a hydrophilic porous polyvinyl alcohol (PVA) hydrogel for natural sweat collection for fingertip touch sweat Cu2+ monitoring. The proposed sensor has several very attractive features: (i) the LIG-In-CdS photoelectrode with high photoelectric conversion efficiency can be produced by a cheap 450 nm semiconductor laser system; (ii) the sensor performs Cu2+ detection with a wide linear range of 1.28 ng/mL~5.12 μg/mL and good selectivity; (iii) the PVA hydrogel possesses an excellent antifouling effect ability and a rapid natural sweat collection ability; and (iv) the sensor exhibits feasibility and good reliability for PEC sensing of sweat Cu2+. Thus, these advantages endow the proposed method with a great deal of potential for smart monitoring of heavy metals in sweat in the future.

Few-layer porous carbon nitride anchoring Co and Ni with charge transfer mechanism for photocatalytic CO2 reduction

The low specific surface area and low charge transfer efficiency of conventional graphite carbon nitride (g-C₃N₄) are the main obstacles to its application in photocatalytic CO₂ reduction. In this paper, graphite carbon nitride was protonated by phosphoric acid (H₃PO₄), and a new few-layer porous carbon nitride was prepared by intercalation polymerization with doping bimetal in the cavity of g-C₃N₄. Under visible light irradiation, the CO formation rate of Co/Ni co-doped g-C₃N₄ can reach 13.55 μmol g^-1 h^-1, which was 3.9 times higher than that of g-C₃N₄ (3.49 μmol g^-1 h^-1). The density functional theory (DFT) calculations showed that the addition of Co and Ni in the cavity of g-C₃N₄ can induce bimetallic synergistic regulation of the electronic structure, thus improving the separation efficiency of charges and visible light capture ability of g-C₃N₄. Our work has great reference value for designing and synthesizing novel bimetallic co-doped g-C₃N₄ photocatalytic materials.

Tailoring g-C3N4 with Lanthanum and Cobalt Oxides for Enhanced Photoelectrochemical and Photocatalytic Activity

Herein, the synthesis, characterization, and photoelectrochemical and photocatalytic characteristics of hydrothermally prepared La2O3–g-C3N4, CoO–g-C3N4, and La2O3–CoO–g-C3N4 are discussed. The XRD analysis and crystalline phases unveiled the impregnation of La2O3 and CoO into g-C3N4. The microscopic analysis supports the formation of g-C3N4 nanoflakes and La2O3 and CoO nanoparticles embedded homogeneously in the La2O3–CoO–g-C3N4 nanocomposite, whereas the EDX comprehended their respective elemental composition and ratios. A bandgap energy of 2.38 eV for La2O3–CoO–g-C3N4 was calculated using the Tauc plot method, complementing high visible-light activity. The solar-driven water-splitting reaction exhibited significant photocurrent efficiency (~3.75 mA/cm2), augmenting the hydrogen generation by La2O3–CoO–g-C3N4 compared to that by pure g-C3N4, La2O3–g-C3N4, and CoO–g-C3N4 in 0.5 M Na2SO4 electrolyte. The synergistic effect of La2O3 and CoO impregnation with g-C3N4 led to effective division of the photogenerated charge transporters, enhancing the photocatalytic hydrogen generation by the photocatalysts. Furthermore, photocatalytic pollutant removal, namely greater than 90% decomposition of methylene blue (MB) from water, was investigated with a pseudo-first-order reaction kinetics under 1 sun visible-light irradiation. Thus, La2O3–CoO–g-C3N4 nanocomposite was found to be a prospective material for harnessing solar energy.

Limbic Inducted and Delocalized Effects of Diazole in Carbon Nitride Skeleton for Propelling Photocatalytic Hydrogen Evolution

Skeleton modification on carbon nitride (g-C₃N₄) via organic molecules is a recognized effective strategy to improve photocatalytic performance because it can powerfully improve charge separation in the skeleton plane. Herein, a diazole with a unique conjugated structure is bonded on edge of the g-C₃N₄ skeleton through a moderate polymerization of urea with 4-aminoantipyrine (4AAP). Meanwhile, the Pt nanoparticles selectively deposit on edge of the g-C₃N₄-4AAP₁₅ nanosheet. It reveals that the robust limbic inducted and delocalized effects of diazole not only facilitate photogenerated electrons aggregation toward skeleton edge to promote in-plane carrier separation but also effectively stabilize and delocalize photogenerated electrons to improve carrier lifetime for propelling the photocatalytic hydrogen evolution (PHE) reaction. Specifically, the PHE rate over optimal g-C₃N₄-4AAP₁₅ (284.2 μmol h^-1) is 10 times that of pure g-C₃N₄ (27.6 μmol h^-1) and the apparent quantum efficiency (AQE) at 420 nm reaches up to 24.2%. Through insights into the functionalized effect of small nitrogenous heterocycles introduced into the skeleton edge of g-C₃N₄, this work opens a new design thought for exploiting high-efficiency g-C₃N₄-based photocatalysts for photocatalytic application.

In situ construction of 0D CoWO4 modified 1D Mn0.47Cd0.53S for boosted visible-light photocatalytic H2 activity and photostability

To enhance the photocatalytic activity, loading proper semiconductor with high efficiency and low cost is one of the most valid approaches. Herein, various amounts of CoWO₄ as a novel metal-free material were loaded on Mn_0.47Cd_0.53S (MCS) nanorods for photocatalytic hydrogen production reaction. The CoWO₄/Mn_0.47Cd_0.53S-25 (CW/MCS-25) exhibits the highest hydrogen production rate of 41.53 mmol·h^-1·g^-1 in the Na₂S/Na₂SO₃ system, which is about 2.68 times higher than that of pristine MCS. The Mapping and HRTEM reveals the deposited of CoWO₄ on the MCS. The detailed analyses of XPS, EIS, TRPL spectra and transient photocurrent responses indicate that CoWO₄ and MCS interacted closely and the photogenerated electrons of CoWO₄ can be transferred into MCS. In particular, the introduction of CoWO₄ can further transfer the photogenerated holes of MCS, thereby inhibiting the photocorrosion of MCS and improving photocatalytic activity. This work provides a reference for the exploration of noble metal-free composite material and shows great potential in the photocatalytic application.

Carbon nanotubes interpenetrating MOFs-derived Co-Ni-S composite spheres with interconnected architecture for high performance hybrid supercapacitor

Recently, carbon nanotubes (CNT)-based interconnected architectures exhibit promising prospects in supercapacitors due to their flexibility and high electrical conductivity. Herein, a three-dimensional (3D) interconnected network structure combined with conductive carbon nanotubes interpenetrating MOFs-derived Co-Ni-S composite spheres (Co-Ni-S/CNTs) was synthesized. Such 3D interconnected architecture significantly leads to a favorable electronic structure, fast charge-transfer capacity, and more pseudocapacitive. The Co-Ni-S/CNTs-based hybrid electrode exhibits an extraordinary specific capacitance of 540.6C g^-1 at 1 A g^-1 and competitive rate performance (capacity retention rate of 69.9% when the current density increases to 10 times). Subsequently, a hybrid supercapacitor is assembled using Co-Ni-S/CNTs as the positive electrode and commercial activated carbon as negative electrode. The device delivers a high energy density of 63.5 W h kg^-1 at 800 W kg^-1 and keeps 83.0% initial capacitance retention after 10,000 cycles. The encouraging performances demonstrate the significant contribution of the 3D interconnected architecture for the future energy storage.

pH-induced hydrothermal synthesis of Bi2WO6 nanoplates with controlled crystal facets for switching bifunctional photocatalytic water oxidation/reduction activity

Bifunctional photocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have attracted growing interest to understand the mechanisms governing different evolution reactions, and the bifunctional activity of a single type of crystalline photocatalyst has gained especial attention. We herein report the high photocatalytic OER and HER activities of Bi₂WO₆ nanoplates (BWO NPs) which are synthesized by a simple hydrothermal method, and the switchable OER and HER performances controlled by the pH value of the precursor solvent. In the pH range from 4 to 9, the thickness of BWO NPs along the [001] direction exhibits interesting dependence on the pH value, which decreases as the pH value increases. Correspondingly, the BWO NPs obtained at the pH value of 7 (BWO-7) show the highest photocatalytic OER activity, while the BWO NPs synthesized at the pH value of 9 (BWO-9) exhibit the highest photoactivity towards HER. The electronic band structure analysis indicates that the highest photocatalytic OER activity is related to the band alignment of the valence band maximum of Bi₂WO₆, which determines the efficient separation of photogenerated electrons and holes as well as the fast charge transfer kinetics. The crystal facet evolution resulting from thickness reduction promotes the exposure of {001} facets for HER and decreases the exposure of {100} and {010} facets for OER. This work provides new insights into the combined effects of crystal facets and electronic band structures on photocatalysis.

Molybdenum impregnated g-C3N4 nanotubes as potentially active photocatalyst for renewable energy applications

Molybdenum (Mo) impregnated g-C3N4 (Mo-CN) nanotubes are fabricated via a thermal/hydrothermal process to augment photoelectrochemical properties during solar-driven water-splitting (SDWS) reactions. Graphitic-C3N4 is an attractive material for photocatalysis because of its suitable band energy, high thermal and chemical stability. The FE-SEM and HR-TEM comprehend the nanotube-like morphology of Mo-CN. The spectroscopic characterization revealed bandgap energy of 2.63 eV with high visible-light activity. The x-ray diffraction of pristine g-C3N4 and Mo-CN nanotubes discloses the formation of triazine-based nanocrystalline g-C3N4, which remains stable during hydrothermal impregnation of Mo. Furthermore, Mo-CN nanotubes possess high sp2-hybridized nitrogen content, and metallic/oxidized Mo nanoparticles (in a ratio of 1:2) are impregnated into g-C3N4. The XPS analysis confirms C, N, and Mo for known atomic and oxidation states in Mo-CN. Furthermore, high photocurrent efficiency (~ 5.5 mA/cm2) is observed from 5%-Mo-CN nanotubes. That displays efficient SDWS by 5%-Mo-CN nanotubes than other counterparts. Impedance spectroscopy illustrated the lowest charge transfer resistance (Rct) of 5%-Mo-CN nanotubes, which further confirms the fast electron transfer kinetics and efficient charge separation resulting in high photocurrent generation. Hence, 5%Mo-CN composite nanotubes can serve as a potential photocatalytic material for viable solar-driven water splitting.

Highly-efficient visible-light-driven photocatalytic H2 evolution integrated with microplastic degradation over MXene/ZnxCd1-xS photocatalyst

The development of highly-efficient photocatalyst for H₂ production integrated with microplastic degradation is significant to meet the demand for clean energy and resolve "white pollution". Herein, a series of MXene/Zn_xCd_1-xS photocatalysts were successfully fabricated for H₂ evolution integrated with degradation of polyethylene terephthalate (PET). The resultant photocatalysts exhibited excellent photocatalytic performance, and the best photocatalytic H₂ evolution rate can reach 14.17 mmol·g^-1·h^-1 in alkaline PET alkaline solution. What's more, the PET was also converted to the useful organic micromolecule, including glycolate, acetate, ethanol, etc. The highly-efficient photocatalytic performance of MXene/Zn_xCd_1-xS photocatalysts can be attributed to the enhanced separation ability of photocarriers and optimum band structure with enhanced oxidation capacity of valence band. Finally, the photocatalytic mechanism was investigated in detail. Overall, this work supplied a new useful guidance for solving the energy problem and microplastic pollution issues, simultaneously.

Supercritically exfoliated Bi2Se3 nanosheets for enhanced photocatalytic hydrogen production by topological surface states over TiO2

Owing to the unique electronic properties of layered materials, topological insulators have interestingly grabbed much attention in the field of photocatalytic water splitting. Nowadays, 2D layered materials were composited with semiconductor photocatalysts, encourage much as it provides enormous active sites and also significantly prevent photogenerated charge recombination. Especially, Bi₂Se₃ possesses exceptional properties like topologically preserved conducting surface states with bulk insulating behavior and high surface area, which provides unconventional electron dynamics, resulting in facile electron transport and effective charge separation to photocatalyst. So far, several methods have been attempted to synthesize few-layered Bi₂Se₃ nanosheets from its bulk crystals. Here, a unique attempt is made and succeeded to exfoliate bulk Bi₂Se₃ to few layered nanosheets via surfactant free supercritical fluid processing using N-Methyl-2-pyrrolidone (NMP) as an exfoliating agent, with a short reaction time of 15 min. The exfoliation of Bi₂Se₃ crystal was confirmed by several characterization techniques, such as XRD, SEM, Raman, and HR-TEM. Furthermore, different weight percentages of exfoliated Bi₂Se₃ sheets/anatase TiO₂ nanoparticles were prepared and examined the photocatalytic activity using glycerol as a hole scavenger. Among them, 15 wt.% Bi₂Se₃ coupled TiO₂ nanocomposite showed enormous hydrogen evolution rate of 84.9 mmol h^-1g^-1_cat, which is 80 times higher than that of TiO₂ nanoparticles. In addition, the photostability of the nanocomposite was also verified, where it retains 94% of activity even after 4 cycles of continuous experiments. The improved rate of H₂ production was understood by theoretical calculations that topologically preserved conducting surface states of co-catalyst, Bi₂Se₃ nanosheets is supported to high mobile and scatter free electrons. It mediates the transport of electrons with TiO₂ nanoparticles that helped the effective charge separation. Thus, it proves a promising candidate for photocatalytic hydrogen production.

In situ construction of multi-dimensional Co3O4/NiCo2O4 hierarchical flakes on self-supporting carbon substrate with ultra-high capacitance for hybrid supercapacitors

Research on environmentally friendly energy storage devices is an important strategy to solve the energy crisis and environmental pollution. Herein, a novel self-supporting electrode based on multi-dimensional Co₃O₄/NiCo₂O₄ hierarchical flakes coating on graphene/carbon sphere (rGO/CS) conductive substrate is reasonably designed. Firstly, a simple hydrothermal method is used to synthesize NiCo₂O₄ with both flake and nanoneedle morphology on the rGO/CS substrate. Subsequently, Co₃O₄/NiCo₂O₄@rGO/CS is obtained by in-situ growth of metal organic frameworks polyhedrons on the surface of NiCo₂O₄ flakes followed by calcination. In the unique structure, benefitting from the synergy between the substrate and multi-element transition metal oxides, the integrated film shows good conductivity, high specific surface area and abundant active sites. Thus, the binder-free electrode exhibits an ultra-high specific capacitance of 3876.6 F g^-1 (538.4 mA h g^-1) at 1 A g^-1. A hybrid supercapacitor is assembled with activated carbon as the negative electrode and Co₃O₄/NiCo₂O₄@rGO/CS as the positive electrode, the device shows a highest energy density of 56.5 Wh kg^-1 at a power density of 800 W kg^-1. After 6000 charge-discharge cycles, 92.5% of the initial capacitance can be still maintained, indicating its good application prospects in energy storage materials.

Photocatalytic Activity of S-Scheme Heterostructure for Hydrogen Production and Organic Pollutant Removal: A Mini-Review

Finding new technologies and materials that provide real alternatives to the environmental and energy-related issues represents a key point on the future sustainability of the industrial activities and society development. The water contamination represents an important problem considering that the quantity and complexity of organic pollutant (such as dyes, pesticides, pharmaceutical active compounds, etc.) molecules can not be efficiently addressed by the traditional wastewater treatments. The use of fossil fuels presents two major disadvantages: (1) environmental pollution and (2) limited stock, which inevitably causes the energy shortage in various countries. A possible answer to the above issues is represented by the photocatalytic technology based on S-scheme heterostructures characterized by the use of light energy in order to degrade organic pollutants or to split the water molecule into its components. The present mini-review aims to outline the most recent achievements in the production and optimization of S-scheme heterostructures for photocatalytic applications. The paper focuses on the influence of heterostructure components and photocatalytic parameters (photocatalyst dosage, light spectra and intensity, irradiation time) on the pollutant removal efficiency and hydrogen evolution rate. Additionally, based on the systematic evaluation of the reported results, several perspectives regarding the future of S-scheme heterostructures were included.

Controlling the coordination environment of Co atoms derived from Co/ZIF-8 for boosting photocatalytic H2 evolution of CdS

Regulating the coordination environment of metal-N_x species by replacing N with low electronegativity atoms is an approach of tuning the electrocatalytic performance of metal-based sites. However, such effects on the enhancement of photocatalytic H₂ evolution over semiconductors are not discussed yet. Herein, we designed and prepared Co-based cocatalysts with controlled coordination environment via calcination Co/ZIF-8 loaded with triphenylphosphine followed by a sulfurization treatment. It was then used as cocatalyst to modify CdS. The effects of the coordination environment of Co atoms on the H₂ evolution activity of CdS were discussed. The obtained Co was co-stabilized by N, P, and S atoms and embedded in graphitic carbon (denoted as Co-N_xPS/C). Experimental results indicated that the Co-N_xPS/C exhibited high activity in enhancing H₂ evolution of CdS with a value of 1260 μmol after 5 h irradiation. The simultaneous replacement of N with P and S atoms in N-stabilized Co embedded in carbon could enhance light harvesting, accelerate the transfer of photogenerated electrons from CdS to carbon with increased electrons accumulation ability and conductivity, improve charge separation efficiency, and enhance proton reduction kinetics. It is believed that the results of this study could promote the development of other high performance MOF-derived atomically dispersed cocatalysts to increase photocatalytic H₂ evolution.

Highly dispersive palladium nanoparticle in nanoconfined spaces for heterogeneous catalytic reduction of anthropogenic pollutants

Pd-containing catalysts are highly promising in catalytic reactions, and their activity severely dependent on the dispersion extent of Pd nanoparticles (Pd NPs) . However, the regulation of Pd NPs size and dispersion degree are now pretty much the agendas. Here we report a facile solid-state fabrication strategy (SSFS) to promote Pd NPs dispersion in the nano environment of as made mesoporous silica KIT-6 (AK) by taking advantage of three critical factors, namely (i) the confined spaces where Pd precursor locate during fabrication, (ii) the interaction between Pd and supports, and (iii) the 3-dimentional (3D) structure of AK. First, AK presents 3D confined spaces between silica walls and template P123. Second, both silica walls and template P123 in AK offer interaction with Pd precursor. Third, the 3D structure provides more easy access for Pd insertion than linear channels structure without any pore blockage. The characterization results revealed that AK give better dispersion with smaller size of (3.9 nm) Pd than its counterpart (16 nm) prepared from template-free KIT-6 (CK). Moreover, the synthesized catalysts exhibit excellent activity and stability in catalytic conversion of p-nitrophenol (p-NP) and Methylene blue (MB). For a typical PdAK-1.0 catalyst, the complete conversion of P-NP and MB was achieved in less than 10 min with a reaction rate constant (k) of 0.3106 and 0.345 min^-1, respectively. It is superior to that on PdCK-1.0 prepared from template free KIT-6 and several reported catalysts. Furthermore, the PdAK-1.0 catalyst presents pretty good stability in catalytic reduction and is apparently better than PdCK-1.0.

Separation of biobutanol from ABE fermentation broth using lignin as adsorbent: A totally sustainable approach with effective utilization of lignocellulose

Adsorption is considered to be a promising butanol recovery method for solving the issue of inhibition in the ABE (acetone-butanol-ethanol) fermentation. As a byproduct in the second generation biobutanol industry, lignin was found to be a good adsorbent for the butanol enrichment. It is conducive to the full utilization of renewable lignocellulose biomass resource. Kinetic and equilibrium experiments indicated that lignin had a satisfactory adsorption rate and capacity that are comparable to those of many synthetic materials. Multicomponent adsorption experiments revealed that lignin had higher adsorption selectivity toward butanol than that of ethanol and acetone. The adsorption capacity of lignin for butanol first increased and then gradually decreased with increasing temperature. And maximum adsorption capacity reached 304.66 mg g^-1 at 313 K. The inflection point of temperature is close to the ABE fermentation temperature of 310 K. The condensed butanol by desorption was 145 g L^-1, with a satisfying regeneration performance. ¹H NMR and FT-IR spectra indicated that the aromatic units of lignin formed π-systems with A/B/E. The π-system is particularly significant for butanol due to its longer hydrocarbon chain. These results could contribute to the emerging lignin-based materials for butanol separation.

Enhanced photoelectrocatalytic performance of α-MnO2 by Sb and N charge compensation

The donor Sb and acceptor N can promote the separation of electron–hole pairs excited by photoirradiation.

Phase transformation and room temperature stabilization of various Bi2O3 nano-polymorphs: effect of oxygen-vacancy defects and reduced surface energy due to adsorbed carbon species

We report the grain growth from the nanoscale to microscale and a transformation sequence from Bi →β-Bi₂O₃→γ-Bi₂O₃→α-Bi₂O₃ with the increase of annealing temperature. The room temperature (RT) stabilization of β-Bi₂O₃ nanoparticles (NPs) was attributed to the effect of reduced surface energy due to adsorbed carbon species, and oxygen vacancy defects may have played a significant role in the RT stabilization of γ-Bi₂O₃ NPs. An enhanced red emission band was evident from all the samples attributed to oxygen-vacancy defects formed during the growth process in contrast with the observed white emission band from the air annealed Bi ingots. Based on our experimental findings, the air annealing induced oxidation of Bi NPs and transformation mechanism within various Bi₂O₃ nano-polymorphs are presented. The outcome of this study suggests that oxygen vacancy defects at the nanoscale play a significant role in both structural stabilization and phase transformation within various Bi₂O₃ nano-polymorphs, which is significant from theoretical consideration.