Ji-Jun Zou

Hollow Cobalt-Based Bimetallic Sulfide Polyhedra for Efficient All-pH-Value Electrochemical and Photocatalytic Hydrogen Evolution

The development of highly active, universal, and stable inexpensive electrocatalysts/cocatalysts for hydrogen evolution reaction (HER) by morphology and structure modulations remains a great challenge. Herein, a simple self-template strategy was developed to synthesize hollow Co-based bimetallic sulfide (MxCo3-xS4, M = Zn, Ni, and Cu) polyhedra with superior HER activity and stability. Homogenous bimetallic metal-organic frameworks are transformed to hollow bimetallic sulfides by solvothermal sulfidation and thermal annealing. Electrochemical measurements and density functional theory computations show that the combination of hollow structure and homoincorporation of a second metal significantly enhances the HER activity of Co3S4. Specifically, the homogeneous doping in Co3S4 lattice optimizes the Gibbs free energy for H* adsorption and improves the electrical conductivity. Impressively, hollow Zn0.30Co2.70S4 exhibits electrocatalytic HER activity better than most of the reported nobel-metal-free electrocatalysts over a wide pH range, with overpotentials of 80, 90, and 85 mV at 10 mA cm(-2) and 129, 144, and 136 mV at 100 mA cm(-2) in 0.5 M H2SO4, 0.1 M phosphate buffer, and 1 M KOH, respectively. It also exhibits photocatalytic HER activity comparable to that of Pt cocatalyst when working with organic photosensitizer (Eosin Y) or semiconductors (TiO2 and C3N4). Furthermore, this catalyst shows excellent stability in the electrochemical and photocatalytic reactions. The strategy developed here, i.e., homogeneous doping and self-templated hollow structure, provides a way to synthesize transition metal sulfides for catalysis and energy conversion.

Water-Mediated Promotion of Dye Sensitization of TiO2 under Visible Light

Preadsorbed water along with surrounding bulk water significantly modulates the surface electronic structure of TiO(2), switches the adsorption mode of dyes, and promotes dye sensitization of TiO(2) under visible-light irradiation. This opens a door toward facile improvement in the efficiency of photodegradation of dyes and dye-sensitized solar cells under visible-light irradiation without any complicated and expensive surface modulation.

Titanium-Defected Undoped Anatase TiO2 with p-Type Conductivity, Room-Temperature Ferromagnetism, and Remarkable Photocatalytic Performance

Defects are critically important for metal oxides in chemical and physical applications. Compared with the often studied oxygen vacancies, engineering metal vacancies in n-type undoped metal oxides is still a great challenge, and the effect of metal vacancies on the physiochemical properties is seldom reported. Here, using anatase TiO2, the most important and widely studied semiconductor, we demonstrate that metal vacancies (VTi) can be introduced in undoped oxides easily, and the presence of VTi results in many novel physiochemical properties. Anatase Ti0.905O2 was synthesized using solvothermal treatment of tetrabutyl titanate in an ethanol-glycerol mixture and then thermal calcination. Experimental measurements and DFT calculations on cell lattice parameters show the unstoichiometry is caused by the presence of VTi rather than oxygen interstitials. The presence of VTi changes the charge density and valence band edge of TiO2, and an unreported strong EPR signal at g = 1.998 presents under room temperature. Contrary to normal n-type and nonferromagnetic TiO2, Ti-defected TiO2 shows inherent p-type conductivity with high charge mobility, and room-temperature ferromagnetism stronger than Co-doped TiO2 nanocrystalline. Moreover, Ti-defected TiO2 shows much better photocatalytic performance than normal TiO2 in H2 generation (4.4-fold) and organics degradation (7.0-fold for phenol), owing to the more efficient charge separation and transfer in bulk and at semiconductor/electrolyte interface. Metal-defected undoped oxides represent a unique material; this work demonstrates the possibility to fabricate such material in easy and reliable way and thus provides new opportunities for multifunctional materials in chemical and physical devices.

Tungsten Oxides for Photocatalysis, Electrochemistry, and Phototherapy.

The conversion, storage, and utilization of renewable energy have all become more important than ever before as a response to ever-growing energy and environment concerns. The performance of energy-related technologies strongly relies on the structure and property of the material used. The earth-abundant family of tungsten oxides (WOx ≤3 ) receives considerable attention in photocatalysis, electrochemistry, and phototherapy due to their highly tunable structures and unique physicochemical properties. Great breakthroughs have been made in enhancing the optical absorption, charge separation, redox capability, and electrical conductivity of WOx ≤3 through control of the composition, crystal structure, morphology, and construction of composite structures with other materials, which significantly promotes the efficiency of processes and devices based on this material. Herein, the properties and synthesis of WOx ≤3 family are reviewed, and then their energy-related applications are highlighted, including solar-light-driven water splitting, CO2 reduction, and pollutant removal, electrochromism, supercapacitors, lithium batteries, solar and fuel cells, non-volatile memory devices, gas sensors, and cancer therapy, from the aspect of function-oriented structure design and control.

Plasma application for more environmentally friendly catalyst preparation

The present status of catalyst preparation using nonthermal plasma treatment has been summarized in this paper. Improved dispersion, better low-temperature activity, enhanced stability, and better anti-carbon deposition performance can be achieved with nonthermal plasma-treated catalysts. The improvement in catalyst preparation with nonthermal plasma treatment can reduce or avoid the use of hazardous chemicals. Nonthermal plasma catalyst treatment has especially induced a new development of nonthermal plasma for catalyst reduction. The reduction using hydrogen at high temperatures or using hazardous liquid chemicals can be replaced by the developed plasma reduction process. The mechanism for nonthermal plasma treatment has been presented. An analog between the man-made gas discharge plasmas and the environment inside the zeolite pores and around catalyst surface defects is also proposed.

Morphology Evolution of TiO2 Facets and Vital Influences on Photocatalytic Activity

Modulation of anatase toward highly active facets has been attracting much attention, but the mechanism and photoactivity are still ambiguous. Here we demonstrate the inherent mechanisms for facets nucleation and morphology evolution, and clarify some vital influences of facets and surface nature on the photoactivity. Simply tuning the Ti/F ratio in the synthetic mixture leads to single anatase crystal exposed with different facets like {001}, {010}, or {110}. And complex sphere structure exposed with {001} facets can be formed by secondary nucleation and growth. Prolonging the hydrothermal treatment time causes selective etching on {001} facets, whereas defluorination via thermal calcination produces many pores on the surface. The photodegradation of positively and negatively charged, and zwitterionic dyes indicates that the type of reactant, adsorption mode and surface area play significant roles in photocatalysis. This work makes a step toward understanding the formation of facet-mediated structure and designing highly active materials for environmental remediation, hydrogen production, and dye-sensitized solar cells.

Silver–Zwitterion Organic–Inorganic Nanocomposite with Antimicrobial and Antiadhesive Capabilities

In this work, we demonstrate a convenient, efficient, and environmentally benign strategy to achieving antimicrobial and antiadhesive purposes using a silver-zwitterion nanocomposite. The synthesis of the nanocomposite relies on loading zwitterionic polymer brushes with Ag(+) precursor ions, followed by their in situ reduction to Ag nanoparticle by ultraviolet (UV) irradiation. Both poly(sulfobetaine methacrylate) (pSBMA) and poly(carboxybetaine methacrylate) (pCBMA) have been studied as matrices for the embedding of silver. Well-dispersed silver nanoparticles are embedded into pCBMA matrices. The obtained pCBMA-silver hybrid (CB-Ag) is capable of killing bacteria upon contact and releasing dead bacteria under wet conditions. Results suggest the feasibility of using this nanocomposite system as a robust and reliable antimicrobial and antiadhesive platform for the prevention of microbial colonization.

Bifunctional catalysts of Co3O4@GCN tubular nanostructured (TNS) hybrids for oxygen and hydrogen evolution reactions

Catalysts for oxygen and hydrogen evolution reactions (OER/HER) are at the heart of renewable green energy sources such as water splitting. Although incredible efforts have been made to develop efficient catalysts for OER and HER, great challenges still remain in the development of bifunctional catalysts. Here, we report a novel hybrid of Co3O4 embedded in tubular nanostructures of graphitic carbon nitride (GCN) and synthesized through a facile, large-scale chemical method at low temperature. Strong synergistic effects between Co3O4 and GCN resulted in excellent performance as a bifunctional catalyst for OER and HER. The high surface area, unique tubular nanostructure, and composition of the hybrid made all redox sites easily available for catalysis and provided faster ionic and electronic conduction. The Co3O4@GCN tubular nanostructured (TNS) hybrid exhibited the lowest overpotential (0.12 V) and excellent current density (147 mA/cm2) in OER, better than benchmarks IrO2 and RuO2, and with superior durability in alkaline media. Furthermore, the Co3O4@GCN TNS hybrid demonstrated excellent performance in HER, with a much lower onset and overpotential, and a stable current density. It is expected that the Co3O4@GCN TNS hybrid developed in this study will be an attractive alternative to noble metals catalysts in large scale water splitting and fuel cells.

Starch-Enhanced Synthesis of Oxygenates from Methane and Carbon Dioxide Using Dielectric-Barrier Discharges

In this work, starch has been used to enhance the oxygenate formation directly from methane and carbon dioxide using dielectric-barrier discharges (DBDs). The use of starch inhibits the formation of liquid hydrocarbons and significantly increases the selectivity of oxygenates. Oxygenates produced include primarily formaldehyde, methanol, ethanol, formic acid, and acetic acid. The total selectivity is about 10–40% with conversion of methane and carbon dioxide of about 20%. Lower methane feed concentration favors the production of oxygenates, and higher feed flow rate leads to higher selectivity of oxygenates in the presence of starch.

Highly selective self-condensation of cyclic ketones using MOF-encapsulating phosphotungstic acid for renewable high-density fuel

Transferring biomass-derived cyclic ketones such as cyclopentanone and cyclohexanone to a mono-condensed product through aldol self-condensation has great potential for the synthesis of a renewable high-density fuel. However, the selectivity is low for numerous catalysts due to the rapid formation of di-condensed by products. Herein, MIL-101-encapsulating phosphotungstic acid is synthesized to catalyze the self-condensation with selectivity of more than 95%. PTA clusters are uniformly dispersed in MOF cages and decrease the empty space (pore size), which provides both acidic sites and shape-selective capability. The optimal PTA amount decreases corresponding to the increase of reactant size. The shape-selectivity is also realized by changing the pore size of MOF such as from MIL-101 to MIL-100. Moreover, the catalyst is resistant to PTA leaching and performs stably after 5 runs. After hydrodeoxygenation of the mono-condensed product, high-density biofuels with densities of 0.867 g ml−1 and 0.887 g ml−1 were obtained from cyclopentanone and cyclohexanone, respectively. This study not only provides a promising route for the production of high-density biofuel but also suggests the advantage of MOF-based catalysts for shape-selective catalysis involving large molecular size.