Sustainable Production of Molybdenum Carbide (MXene) from Fruit Wastes for Improved Solar Evaporation.

Invited for the cover of this issue is the group of Edison Huixiang Ang at the National Institute of Education, an institute of Nanyang Technological University, Singapore. The image depicts the sustainable fabrication of two-dimensional MXene sheets from the upcycling of fruit waste for solar desalination. Read the full text of the article at 10.1002/chem.202203184.

Unexpected Intrinsic Catalytic Function of Porous Boron Nitride Nanorods for Highly Efficient Peroxymonosulfate Activation in Water Treatment.

Porous boron nitride (BN) nanorods, which were synthesized via a one-stage pyrolysis, exhibited excellent catalytic performance for organics' degradation via peroxymonosulfate (PMS) activation. The origin of the unexpected catalytic function of porous BN nanorods was proposed, in which non-radical oxidation driven by the defects on porous BN dominated the sulfamethoxazole degradation via the generation of singlet oxygen (1O2). The adsorption energy between PMS and BN was calculated via density functional theory (DFT), and the PMS activation kinetics were further investigated using an electrochemical methodology. The evolution of 1O2 was verified by electron spin resonance (ESR) and chemical scavenging experiments. The observed non-radical oxidation presented a high robustness in different water matrices, combined with a series of much less toxic intermediates. The used BN was easily regenerated by heating in air, in which the B-O bond was fully recovered. These findings provide new insights for BN as a non-metal catalyst for organics' degradation via PMS activation, in both theoretical and practical prospects.

Nd-Nb Co-doped SnO2/α-WO3 Electrochromic Materials: Enhanced Stability and Switching Properties.

The fabrication of Nd-Nb co-doped SnO2/α-WO3 electrochromic (EC) materials for smart window applications is presented in the present paper. Nb is a good dopant candidate for ECs owing to its ability to introduce active sites on the surface of α-WO3 without causing much lattice strain due to the similar ionic radius of Nb5+ and W6+. These active sites introduce more channels for charge insertion or removal during redox reactions, improving the overall EC performance. However, Nb suffers from prolonged utilization due to the Li+ ions trapped within the ECs. By coupling Nd with Nb, the co-dopants would transfer their excess electrons to SnO2, improving the electronic conductivity and easing the insertion and extraction of Li+ cations from the ECs. The enhanced Nd-Nb co-doped SnO2/α-WO3 exhibited excellent visible light transmission (90% transmittance), high near-infrared (NIR) contrast (60% NIR modulation), rapid switching time (∼1 s), and excellent stability (>65% of NIR modulation was retained after repeated electrochemical cycles). The mechanism of enhanced EC performance was also investigated. The novel combination of Nd-Nb co-doped SnO2/α-WO3 presented in this work demonstrates an excellent candidate material for smart window applications to be used in green buildings.

Spatial confinement of cobalt crystals in carbon nanofibers with oxygen vacancies as a high-efficiency catalyst for organics degradation.

Catalytic activation of peroxymonosulfate (PMS) to generate radicals has received considerable and increasing attention in the environmental catalysis for treatment of recalcitrant pollutants. In the current study, a series of highly porous, cobalt-loaded activated carbon nanofibers (Co/CNFs) were prepared by one-pot electrospinning followed by thermal treatment. Observations showed that the limited addition of Co (≤8%) had no obvious effect on the morphology of the resulted CNFs, but it did affect the surface area and porosity of the CNFs as well as the carbon graphitic process during the carbonization. The applicability of this confined nanoreactor used in sulfate-radical based advanced oxidation processes (SR-AOPs) was systematically investigated. The effect of pH on the radical generation and organics removal was examined. The oxygen species on the CNFs played an important role in the activation of PMS. The carbon layer encapsulated on the Co crystal surface inhibited the Co leaching during the reaction and increased the catalytic efficiency due to the enhanced interfacial charge transfer. Meanwhile, the carbon layer could synchronously function as the adsorptive active sites during the degradation of organics. Results showed that the Co/CNFs possessed the highest catalytic efficiency under neutral pH, corresponding to the sulfate radical generation. The Co leaching and XPS results showed that the Co served as the main active site in PMS activation.

Rational design of hierarchically-structured CuBi2O4 composites by deliberate manipulation of the nucleation and growth kinetics of CuBi2O4 for environmental applications.

A versatile, eco-friendly synthesis scheme was developed to fabricate a series of hierarchically-structured CuBi2O4 composites for environmental applications. By simple tuning of the synthesis protocol (i.e. controlling the ethylene glycol to water ratio in the reaction matrix and employing different auxiliary metal precursors consisting of Cu(2+), Co(2+) or Fe(3+) species), deposition of various metal oxides on CuBi2O4 was achieved. The proposed one-pot synthesis protocol utilizes the fast nucleation and controlled growth kinetics of CuBi2O4 to deliberately immobilize the desired metal oxides on the surface of the CuBi2O4. The manipulation of the diffusion rate, mass transfer kinetics and atomic mobility of the metal precursors by controlling the viscosity and dielectric properties of the reaction matrix lead to the formation of different CuBi2O4 composites with the desired properties. The synergistic coupling effect between the CuBi2O4 and deposited metal oxide contributed to the superior performance of the novel CuBi2O4 composites. The CuBi2O4 composites demonstrate excellent potential for various environmental applications such as being a catalyst for generating sulfate radicals from peroxymonosulfate for organic pollutant removal in water and being a disinfectant. The proposed green synthesis protocol is simple and offers flexibility for fabricating hierarchically-structured CuBi2O4 composites with enhanced properties for targeted applications.

Performance of magnetic activated carbon composite as peroxymonosulfate activator and regenerable adsorbent via sulfate radical-mediated oxidation processes.

Magnetic activated carbon composite (CuFe2O4/AC, MACC) was prepared by a co-precipitation-calcination method. The MACC consisted of porous micro-particle morphology with homogeneously distributed CuFe2O4 and possessed high magnetic saturation moment (8.1 emu g(-1)). The performance of MACC was evaluated as catalyst and regenerable adsorbent via peroxymonosulfate (PMS, Oxone(®)) activation for methylene blue (MB) removal. Optimum CuFe2O4/AC w/w ratio was 1:1.5 giving excellent performance and can be reused for at least 3 cycles. The presence of common inorganic ions, namely Cl(-) and NO3(-) did not exert significant influence on MB degradation but humic acid decreased the MB degradation rate. As a regenerable adsorbent, negligible difference in regeneration efficiency was observed when a higher Oxone(®) dosage was employed but a better efficiency was obtained at a lower MACC loading. The factors hindering complete MACC regeneration are MB adsorption irreversibility and AC surface modification by PMS making it less favorable for subsequent MB adsorption. With an additional mild heat treatment (150 °C) after regeneration, 82% of the active sites were successfully regenerated. A kinetic model incorporating simultaneous first-order desorption, second-order adsorption and pseudo-first order degradation processes was numerically-solved to describe the rate of regeneration. The regeneration rate increased linearly with increasing Oxone(®):MACC ratio. The MACC could potentially serve as a catalyst for PMS activation and regenerable adsorbent.

A novel three-dimensional spherical CuBi2O4 consisting of nanocolumn arrays with persulfate and peroxymonosulfate activation functionalities for 1H-benzotriazole removal.

A novel CuBi2O4 consisting of self-assembled spherical nanocolumn arrays (CuB-H) was synthesized via a facile hydrothermal method. It was further modified by controlling the Cu : Bi ratio during synthesis to become an efficient bi-functional catalyst (CuB-2.5) activated persulfate (PS) and peroxymonosulfate (PMS) for 1H-benzotriazole (BTZ) removal. Characterization of CuB-2.5 using XRD, FESEM, FTIR, BET and XPS revealed that it was morphologically similar to CuB-H and the molecular formula, as determined from the XRD results, was Cu1.2Bi1.6O3.6 with 2.4% w/w of CuO. The CuB-2.5 catalyst exhibited superior performance for BTZ removal via PS and PMS activations over the Cu(2+) (aq.), CuO, CuBi2O4 (CuB-M, microsphere) and CuB-H. The performance of CuB-2.5 was investigated at different initial PS/PMS dosages, initial catalyst loadings and initial BTZ concentrations. Interestingly, it was found that the inter- and intra-molecular hydrogen bondings play prominent roles in the BTZ removal mechanism in both the PS and PMS systems. Meanwhile, it is relatively easy to activate PMS, leading to a faster BTZ removal rate over the PS system. The intermediate products of BTZ degradation produced from the PS and PMS systems were similar, indicating a similar degradation pathway. The catalyst could still retain its morphology and can be reused multiple times.

Colloidal nanocrystals of orthorhombic Cu2ZnGeS4: phase-controlled synthesis, formation mechanism and photocatalytic behavior.

The orthorhombic polymorph of Cu2ZnGeS4 (CZGS) is a metastable wurtzite-derived phase that can only be prepared in the bulk form by extensive heating at high temperatures (≥790 °C) when using the conventional solid-state reaction route. By employing a facile solution-based synthetic strategy, we were able to obtain phase-pure orthorhombic CZGS in nanocrystalline form at a much lower reaction temperature. Prior to this work, the colloidal synthesis of single-phase orthorhombic CZGS on the nanoscale has never been reported. We find that the use of an appropriate combination of coordinating solvents and precursors is crucial to the sole formation of this metastable phase in solution. A possible formation mechanism is proposed on the basis of our experimental results. Because CZGS consists of environmentally benign metal components, it is regarded as a promising alternative material to the technologically useful yet toxic cadmium-containing semiconductors. The orthorhombic CZGS nanocrystals display strong photon absorption in the visible spectrum and are photocatalytically active in dye degradation under visible-light illumination.

Dye removal by surfactant encapsulated polyoxometalates.

A novel surfactant encapsulated polyoxometalate (SEP) has been synthesized by using a simple ion-exchange reaction. The prepared SEP complex was found to self-assemble into nanospherical particles whose morphology and component were characterized by TEM and XPS. The SEP was further incorporated into polyvinylidene fluoride (PVDF) to fabricate SEP incorporated composite membrane (SEP-M). Both the SEP and SEP-M exhibited excellent dye removal activities, which is for the first time reported as an intriguing property of the SEP. A regeneration scheme for SEP-M was successfully proposed without any loss of dye removal efficiency. Detailed mechanism studies were carried out to elucidate the nature of dye decolorization. Ion exchange was revealed to play a dominant role in the dye removal process. The current research not only renders a new example for the simple and direct synthesis of SEP but more importantly provides an efficient dye removal methodology.