In Situ Visual Observation of Surface Energy-Controlled Heterogeneous Nucleation of Metal Nanocrystals.

Electrochemical growth of metal nanocrystals is pivotal for material synthesis, processing, and resource recovery. Understanding the heterogeneous interface between electrolyte and electrode is crucial for nanocrystal nucleation, but the influence of this interaction is still poorly understood. This study employs advanced in situ measurements to investigate the heterogeneous nucleation of metals on solid surfaces. By observing the copper nanocrystal electrodeposition, an interphase interaction-induced nucleation mechanism highly dependent on substrate surface energy is uncovered. It shows that a high-energy (HE) electrode tended to form a polycrystalline structure, while a low-energy (LE) electrode induced a monocrystalline structure. Raman and electrochemical characterizations confirmed that HE interface enhances the interphase interaction, reducing the nucleation barrier for the sturdy nanostructures. This leads to a 30.92-52.21% reduction in the crystal layer thickness and a 19.18-31.78% increase in the charge transfer capability, promoting the formation of a uniform and compact film. The structural compactness of the early nucleated crystals enhances the deposit stability for long-duration electrodeposition. This research not only inspires comprehension of physicochemical processes correlated with heterogeneous nucleation, but also paves a new avenue for high-quality synthesis and efficient recovery of metallic nanomaterials.

Sodium-Directed Photon-Induced Assembly Strategy for Preparing Multisite Catalysts with High Atomic Utilization Efficiency.

Integrating different reaction sites offers new prospects to address the difficulties in single-atom catalysis, but the precise regulation of active sites at the atomic level remains challenging. Here, we demonstrate a sodium-directed photon-induced assembly (SPA) strategy for boosting the atomic utilization efficiency of single-atom catalysts (SACs) by constructing multifarious Au sites on TiO2 substrate. Na+ was employed as the crucial cement to direct Au single atoms onto TiO2, while the light-induced electron transfer from excited TiO2 to Au(Na+) ensembles contributed to the self-assembly formation of Au nanoclusters. The synergism between plasmonic near-field and Schottky junction enabled the cascade electron transfer for charge separation, which was further enhanced by oxygen vacancies in TiO2. Our dual-site photocatalysts exhibited a nearly 2 orders of magnitude improvement in the hydrogen evolution activity under simulated solar light, with a striking turnover frequency (TOF) value of 1533 h-1 that exceeded other Au/TiO2-based photocatalysts reported. Our SPA strategy can be easily extended to prepare a wide range of metal-coupled nanostructures with enhanced performance for diverse catalytic reactions. Thus, this study provides a well-defined platform to extend the boundaries of SACs for multisite catalysis through harnessing metal-support interactions.

Electrically Controlled Adsorptive Membranes with Tunable Affinity for Selective Chromium (VI) Separation from Water.

Ionic contaminants such as Cr(VI) pose a challenge for water purification using membrane-based processes. However, existing membranes have low permeability and selectivity for Cr(VI). Therefore, in this study, we prepared an electrically controlled adsorptive membrane (ECAM-L) by coating a loose Cl--doped polypyrrole layer on a carbon nanotube substrate, and we evaluated the performance of ECAM-L for Cr(VI) separation from water. We also used electrochemical quartz crystal microbalance measurements and molecular dynamics and density functional theory calculations to investigate the separation mechanisms. The adsorption and desorption of Cr(VI) could be modulated by varying the electrostatic interactions between ECAM-L and Cr(VI) via potential control, enabling the cyclic use of the ECAM-L without additional additives. Consequently, the oxidized ECAM-L showed high Cr(VI) removal performance (<50 µg/L) and treatment capacity (>3500 L/m2) at a high water flux (283 L/m2/h), as well as reusability after the application of a potential. Our study demonstrates an efficient membrane design for water decontamination that can selectively separate Cr(VI) through a short electric stimulus.

Electrically Redox-Active Membrane with Switchable Selectivity to Contaminants for Water Purification.

Membrane technology provides an attractive approach for water purification but faces significant challenges in separating small molecules due to its lack of satisfactory permselectivity. In this study, a polypyrrole-based active membrane with a switchable multi-affinity that simultaneously separates small ionic and organic contaminants from water was created. Unlike conventional passive membranes, the designed membrane exhibits a good single-pass filtration efficiency (>99%, taking 1-naphthylamine and Pb2+ as examples) and high permeability (227 L/m2/h). Applying a reversible potential can release the captured substances from the membrane, thus enabling membrane regeneration and self-cleaning without the need for additives. Advanced characterizations reveal that potential switching alters the orientation of the doped amphipathic molecules with the self-alignment of the hydrophobic alkyl chains or the disordered sulfonate anions to capture the target organic molecules or ions via hydrophobic or electrostatic interactions, respectively. The designed smart membrane holds great promise for controllable molecular separation and water purification.

Revealing the Pore Size-Dependent Sorption Mechanism of Toluene and Cetane in Porous Carbon by Nuclear Magnetic Resonance.

The adsorption of contaminants by porous carbon has been extensively studied by conventional isotherm and kinetic methods. However, the co-adsorption behavior and sorption sites of multiple contaminants in different-sized pores remain unclear. Herein, the nuclear magnetic resonance (NMR) approach is performed to investigate the adsorption mechanism of toluene and cetane in the confined space of carbon at the molecular level. The ring current effect induces the variation in the NMR chemical shifts of in-pore adsorbed toluene and cetane, realizing the identification of pore-dependent adsorption sites for contaminant removal. Cetane has a slower adsorption kinetic but a higher binding energy than toluene, which could squeeze toluene from micropores to larger pores with increasing adsorption quantity. This leads to a stronger competitive adsorption effect in small micropores than in mesopores. Accordingly, hierarchical porous carbons are determined to be the most effective adsorbents for the adsorption of coexisting contaminants. This study not only provides an effective NMR method to reveal the adsorption mechanism in the confined space of porous carbon at the molecular level but also offers new insights into the pore size-dependent adsorption of activated carbon for petroleum contaminant treatment.

Combining non-thermal plasma technology with photocatalysis: a critical review.

Due to the excellent application prospects in the fields of new energy generation and environmental remediation, photocatalysis technology has attracted the increasing attention of researchers. Although significant progress has been made in the past decades, the practical application of this technology is still restricted by the moderate catalytic efficiency. To improve the performance of catalysts, new methods are extremely required for the controllable synthesis of high-efficiency catalysts. To further comprehend the relationship between material structure and catalytic activity, the surface active sites of catalysts should be regulated at the atomic and molecular levels. As the fourth state of matter, plasma can generate diverse active species with low energy consumption. As a subset of plasmas, non-thermal plasma (NTP), defined by the great temperature difference between ions (near room temperature) and electrons (usually hotter than 2 orders of magnitude), contributes to the rapid synthesis of functional nanomaterials under relatively mild conditions. Furthermore, NTP has been widely used for the surface modification of materials. Therefore, the combination of NTP and photocatalysis is expected to provide an ideal approach to synthesize high-performance catalysts and precisely customize their surface structures, which is becoming a new direction in the field of catalysis research. This paper fundamentally reviews the progress in the combination of NTP with photocatalysis for versatile applications. Beginning with the principles of photocatalysis and plasma technology, the application of NTP for catalyst synthesis, the plasma-assisted modification of surface actives sites, and the impact of plasma-involved processes on the catalytic performance are discussed, which will provide useful insights into the performance enhancement of catalysts via plasma-assisted processes.

Mimicking Photosynthesis: A Natural Z-Scheme Photocatalyst Constructed from Red Mud Bauxite Waste for Overall Water Splitting.

All-solid-state Z-Scheme photocatalysts have attracted significant attention due to their great potential for solar fuel production. However, delicately coupling two individual semiconductors with a charge shuttle by a material strategy remains a challenge. Herein, we demonstrate a new protocol of natural Z-Scheme heterostructures by strategically engineering the component and interfacial structure of red mud bauxite waste. Advanced characterizations elucidated that the hydrogen-induced formation of metallic Fe enabled the effective Z-Scheme electron transfer from γ-Fe2 O3 to TiO2 , leading to the significantly boosted spatial separation of photo-generated carriers for overall water splitting. To the best of our knowledge, it is the first Z-Scheme heterojunction based on natural minerals for solar fuel production. Thus our work provides a new avenue toward the utilization of natural minerals for advanced catalysis applications.

Insight into the Key Role of Cr Intermediates in the Efficient and Simultaneous Degradation of Organic Contaminants and Cr(VI) Reduction via g-C3N4-Assisted Photocatalysis.

Photocatalysis provides an impetus for the synergetic removal of Cr(VI) and organic contaminants, but the generation of Cr intermediates and their potential oxidizability may be overlooked in pollutant conversion. Herein, the Cr intermediates in the Cr(VI) reduction process were emphasized in Cr(VI)/bisphenol A (BPA) by using graphitic carbon nitride as a photocatalyst. The active species for BPA photodegradation in the BPA system and Cr(VI)/BPA system suggested that the Cr(VI) reduction process indeed promotes BPA photodegradation. Electron paramagnetic resonance (EPR) of Cr complexes and in situ variable-temperature EPR analysis demonstrated Cr(V) intermediate (g = 1.978) generation in Cr(VI) reduction and its oxidization for BPA degradation in photocatalysis. By adding the electron donor Na2SO3, BPA degradation was induced in Cr(VI)/BPA solution, further confirming the positive effect of Cr(V). Moreover, the difference in BPA degradation products in the BPA/air, Cr(VI)/BPA/air, and Cr(VI)/BPA/Ar systems indirectly explained why the Cr(V) intermediate was involved in BPA degradation. Density functional theory calculations revealed that photogenerated electrons can reduce the free energy (0.98 eV) of converting Cr(VI) into Cr(V), which can facilitate the subsequent Cr(V) oxidation step for BPA degradation. This work contributes to the exploration of the Cr(VI) reduction process and the synergistic removal of organic pollutants in Cr(VI)/organics systems.

Facilitating Molecular Activation and Proton Feeding by Dual Active Sites on Polymeric Carbon Nitride for Efficient CO2 Photoreduction.

Photoreduction of CO2 provides an appealing way to alleviate the energy crisis and manage the global carbon balance but is limited by the high activation energy and the rate-limiting proton transfer. We now develop a dual-site strategy for high-efficiency CO2 conversion through polarizing CO2 molecules at pyridine N vacancies and accelerating the intermediate protonation by protonated pyridine N adjacent to nitrogen vacancies on polymeric carbon nitride. Our photocatalysts with atomic-level engineered active sites manifest a high CO production rate of 1835 µmol g-1 h-1 , 183 times higher than the pristine bulk carbon nitride. Theoretical prediction and experimental studies confirm that such excellent performance is attributed to the synergistic effect between vacant and protonated pyridine N in decreasing the formation energy of the key *COOH intermediates and the efficient electron transfer relay facilitated by the defect-induced shallow trap state and homogeneous charge mediators.

Visualizing the Interfacial Charge Transfer between Photoactive Microcystis aeruginosa and Hydrogenated TiO2.

Exploring photoactive biotic-abiotic conjugations is of great importance for a variety of applications, but it remains difficult to probe the interfacial transfer of photoinduced charge carriers. In this work, Kelvin probe force microscopy, together with fluorescence imaging technique, were used to visually observe the spatial distribution and interfacial behavior of photocarriers in Microcystis aeruginosa/TiO2 hybrids. Experimental investigations suggested that photosynthetic microalgae cells were prone to trap photoholes from TiO2 photocatalysts. Oxygen vacancy defects in semiconductor exhibited significant impact on the charge migration, as the surface photovoltage of hydrogenated TiO2/microalgae hybrid was much higher than the pristine system. Profiting from the bioenhanced charge separation, biotic-abiotic architecture presented remarkably increased activity for photocatalytic inactivation of microalgae microorganisms. This work not only highlights the visual techniques for understanding the charge transfer around biotic-abiotic interface, but also provides a bioenhanced conjugation for the photocatalytic elimination of microorganisms in water treatment applications.

Defect-enhanced photocatalytic removal of dimethylarsinic acid over mixed-phase mesoporous TiO2.

Much attention has been paid to the pollutant dimethylarsenic acid (DMA), because of its high toxicity even at very low doses. Although TiO2 photocatalytic oxidation (PCO) is one of the few effective methods for treating DMA-containing water, the efficient decomposition of DMA and simultaneous removal of toxic arsenic species remains a significant but challenging task. Here, defective mesoporous TiO2 with mixed-phase structure was synthesized and used as both photocatalyst and adsorbent for DMA removal. Due to the reduced band-gap and enhanced separation of photogenerated charge carriers, the oxygen-deficient TiO2 nanostructures exhibited 4.2 times higher PCO efficiency than commercial TiO2 (P25). More importantly, the high surface area of the mesoporous TiO2 provided sufficient active sites for in-situ adsorption and reaction, resulting in the efficient removal of as-formed As(V). Combining the experimental and characterization results, the different roles of reactive species during PCO reactions were clarified. In the presence of hole (h+) as the dominant oxidation species, DMA was demethylated and transformed into MMA. Thereafter, MMA was subsequently reduced to As(III) by photo-generated electrons. Superoxide radicals (O2•-) played a significant role in oxidizing As(III) into As(V), which was finally adsorptively removed by the mesoporous TiO2.

Effect of Single-Atom Cocatalysts on the Activity of Faceted TiO2 Photocatalysts.

The synergetic contribution of crystal facets and atomic cocatalysts toward the photoactivity of TiO2 was fundamentally investigated. Atomic-level dispersed Pt and Au were deposited onto 001-faceted and 101-faceted TiO2, separately. When used as photocatalysts for photocatalytic H2 production, Pt/TiO2-001 showed 1156 and 3 times higher H2 evolution rate than that of cocatalyst-free TiO2-001 and Pt-cocatalyzed TiO2-101. The significantly improved photocatalytic performance was attributed to the efficient separation of high-energy electrons and the sufficient exposure of reactive sites. This study demonstrates a promising way to design single-atom-assisted photocatalysts for high-efficiency water splitting.

Hydrogen-Bond-Mediated Self-Assembly of Carbon-Nitride-Based Photo-Fenton-like Membranes for Wastewater Treatment.

Graphitic carbon nitride has emerged as a promising material for high-performance membranes with both filtration and catalytic abilities. However, the scalable construction of carbon-nitride-based membranes is seriously restricted by the poor ability to tailor the structure and poor solvent solubility of bulk nanostructures. Herein, carbon nitride sol was prepared in high yield and used as a precursor to assemble photo-Fenton-like membranes. Intermolecular hydrogen-bond interactions between carbon nitride nanofibers were found to be vitally important for the repolymerization of hydrolyzed molecules into dense and solid membranes. Intercalated Fe-containing polyoxometalates (Fe-POMs) not only acted as molecular linkers to construct carbon nitride membranes but also provided new opportunities for the catalytic functionality. Benefiting from the hydrophobic nanocapillaries in 2D carbon nitride for ultralow water-carbon friction, self-assembled membranes effectively rejected pollutant molecules with high water permeation flux. The integration of carbon nitride photocatalysts with Fenton-like Fe-POMs contributed to the in situ degradation of retained pollutants. Thus, our work manifested a facile bottom-up strategy to construct photo-Fenton-like membranes with antifouling abilities for wastewater treatment.

Electroactive Modified Carbon Nanotube Filter for Simultaneous Detoxification and Sequestration of Sb(III).

Herein, we rationally designed a dual-functional electroactive filter system for simultaneous detoxification and sequestration of Sb(III). Binder-free and nanoscale TiO2-modified carbon nanotube (CNT) filters were fabricated. Upon application of an external electrical field, in situ transformation of Sb(III) to less toxic Sb(V) can be achieved, which is further sequestered by TiO2. Sb(III) removal kinetics and capacity increase with applied voltage and flow rate. This can be explained by the synergistic effects of the filter's flow-through design, electrochemical reactivity, small pore size, and increased number of exposed sorption sites. STEM characterization confirms that Sb were mainly sequestered by TiO2. XPS, AFS, and XAFS results verify that the Sb(III) conversion process was accelerated by the electrical field. The proposed electroactive filter technology works effectively across a wide pH range. The presence of sulfate, chloride, and carbonate ions negligibly inhibited Sb(III) removal. Exhausted TiO2-CNT filters can be effectively regenerated using NaOH solution. At 2 V, 100 µg/L Sb(III)-spiked tap water generated ∼1600 bed volumes of effluent with >90% efficiency. Density functional theory calculations suggest that the adsorption energy of Sb(III) onto TiO2 increases (from -3.81 eV to -4.18 eV) and Sb(III) becomes more positively charged upon application of an electrical field.

Interfacial Charge Transfer in MoS2/TiO2 Heterostructured Photocatalysts: The Impact of Crystal Facets and Defects.

One of the most challenging issues in photocatalytic hydrogen evolution is to efficiently separate photocharge carriers. Although MoS2 loading could effectively improve the photoactivity of TiO2, a fundamental understanding of the charge transfer process between TiO2 and MoS2 is still lacking. Herein, TiO2 photocatalysts with different exposed facets were used to construct MoS2/TiO2 heterostructures. XPS, ESR, together with PL measurements evidenced the Type II electron transfer from MoS2 to {001}-TiO2. Differently, electron-rich characteristic of {101}-faceted TiO2 were beneficial for the direct Z-scheme recombination of electrons in TiO2 with holes in MoS2. This synergetic effect between facet engineering and oxygen vacancies resulted in more than one order of magnitude enhanced hydrogen evolution rate. This finding revealed the elevating mechanism of constructing high-performance MoS2/TiO2 heterojunction based on facet and defect engineering.

Hierarchical Nanotubular Anatase/Rutile/TiO2(B) Heterophase Junction with Oxygen Vacancies for Enhanced Photocatalytic H2 Production.

Oxygen vacancies have been demonstrated to enhance the interfacial charge separation in TiO2-based photocatalysts. In this report, we explored a facile route to synthesize hierarchical nanotubular anatase/rutile/TiO2(B) nanostructures with high surface area and defective electronic structure. The formation of oxygen vacancies in the heterophase junction was analyzed by UV-vis absorption spectra, electron spin resonance, and X-ray photoelectron spectroscopy. The enhanced interfacial charge separation and transportation ensured the excellent photoactivity of oxygen-deficient junctions for the photocatalytic production of hydrogen. As a result, the defective anatase/rutile/TiO2(B) junction showed a high hydrogen evolution rate of 2.79 mmol/h, which was 19 times higher than blank TiO2 nanotubes. The results demonstrate that defect modulation is a powerful tool to enhance the catalytic performances of TiO2-based photocatalysts.

The synergetic effects of Ti3C2 MXene and Pt as co-catalysts for highly efficient photocatalytic hydrogen evolution over g-C3N4.

Co-catalyst loading provides an effective way to enhance the efficiency of photocatalysts for solar hydrogen production. From a sustainability point of view, it has immense scientific and technological values to explore more efficient co-catalytic systems by using multi-cocatalysts, because of potential synergetic effects between different components. Herein, the feasibility of using Ti3C2 MXene nanoparticles and Pt nanoclusters as dual co-catalysts to enhance the photoactivity of g-C3N4 for H2 production was investigated. Due to the improved electrical conductivity and increased reactive sites for photoreduction reactions, Ti3C2 and Pt co-modified photocatalysts exhibited a high photocatalytic hydrogen production activity of 5.1 mmol h-1 g-1. Compared to g-C3N4/Ti3C2 and g-C3N4/Pt, the 3- and 5-fold increased photoactivity demonstrated great potential of Ti3C2 MXene nanoparticles to construct high-performance photocatalysts. The synergetic effects between Ti3C2 and Pt were fundamentally investigated, indicating that the specific transfer of electrons not only contributed to the inhibited recombination of charge carriers but also resulted in good stability of heterostructured photocatalysts. Our results have demonstrated an approach worthy for the design and fabrication of high-efficiency heterostructures with superior photoactivity for hydrogen energy production.

Enhanced Electroreductive Removal of Bromate by a Supported Pd-In Bimetallic Catalyst: Kinetics and Mechanism Investigation.

In this work, the electroreductive removal of bromate by a Pd1-In4/Al2O3 catalyst in a three-dimensional electrochemical reactor was investigated. A total of 96.4% of bromate could be efficiently reduced and completely converted into bromide within 30 min under optimized conditions. On the basis of the characterization results and kinetics analysis, a synergistic effect of Pd and In was observed, and Pd1-In4/Al2O3 had the highest reaction rate constant of 0.1275 min-1 (vs 0.0413, 0.0328, and 0.0253 min-1 for In/Al2O3, Pd/Al2O3, and Al2O3). The results of electron spin resonance and scavenger experiments confirmed that both direct electron transfer and indirect reduction by atomic H* were involved in the bromate removal process, while the direct reduction played a more important role. Moreover, the introduction of In could increase the zeta potential of Pd1-In4/Al2O3, facilitating bromate adsorption and its subsequent reduction on the catalyst. Finally, a reaction mechanism for bromate reduction by Pd1-In4/Al2O3 was proposed based on all the experimental results.

Biomolecule-assisted synthesis of defect-mediated Cd1-xZnxS/MoS2/graphene hollow spheres for highly efficient hydrogen evolution.

Moderate efficiency and the utilization of noble metal cocatalysts are the key factors that restrict the large-scale application of photocatalytic hydrogen production. To develop more efficient photocatalysts based on earth abundant elements, either a new material strategy or a fundamental understanding of the semiconductor/cocatalyst interfaces is highly desirable. In this paper, we studied the feasibility of in situ formation of defect-rich cocatalysts on graphene-based photocatalysts. A facile biomolecule-assisted strategy was used to self-assmble Cd1-xZnxS/MoS2/graphene hollow spheres. The defect-mediated cocatalyst and synergetic charge transfer around heterostructured interfaces exhibit a significant impact on the visible-light-driven photocatalytic activity of multicomponent solid solutions. With engineered interfacial defects, Cd0.8Zn0.2S/MoS2/graphene hollow spheres exhibited a 63-fold improved H2 production rate, which was even 2 and 3.8 times higher than those of CdS/MoS2/graphene hollow spheres and Cd0.8Zn0.2S/Pt. Therefore, our research provides a promising approach for the rational design of high-efficiency and low-cost photocatalysts for solar fuel production.

Cu(2)ZnSnS(4)-Pt and Cu(2)ZnSnS(4)-Au heterostructured nanoparticles for photocatalytic water splitting and pollutant degradation.

Cu2ZnSnS4, based on abundant and environmental friendly elements and with a direct band gap of 1.5 eV, is a main candidate material for solar energy conversion through both photovoltaics and photocatalysis. We detail here the synthesis of quasi-spherical Cu2ZnSnS4 nanoparticles with unprecedented narrow size distributions. We further detail their use as seeds to produce CZTS-Au and CZTS-Pt heterostructured nanoparticles. Such heterostructured nanoparticles are shown to have excellent photocatalytic properties toward degradation of Rhodamine B and hydrogen generation by water splitting.