Interplay between Defects and Short-Range Disorder Manipulating the Oxygen Evolution Reaction on a Layered Double Hydroxide Electrocatalyst.

Improving the efficiency of the oxygen evolution reaction (OER) is crucial for advancing sustainable and environmentally friendly hydrogen energy. Layered double hydroxides (LDHs) have emerged as promising electrocatalysts for the OER. However, a thorough understanding of the impact of structural disorder and defects on the catalytic activity of LDHs remains limited. In this work, a series of NiAl-LDH models are systematically constructed, and their OER performance is rigorously screened through theoretical density functional theory. The acquired results unequivocally reveal that the energy increase induced by structural disorder is effectively counteracted at the defect surface, indicating the coexistence of defects and disorder. Notably, it is ascertained that the simultaneous presence of defects and disorder synergistically augments the catalytic activity of LDHs in the context of the OER. These theoretical findings offer valuable insights into the design of highly efficient OER catalysts while also shedding light on the efficacy of LDH electrocatalysts.

Promoting Electrocatalytic Hydrogenation of Oxalic Acid to Glycolic Acid via an Al3+ Ion Adsorption Strategy Coupled with Ethylene Glycol Oxidation.

Electrocatalytic hydrogenation (ECH) of oxalic acid (OX) to produce glycolic acid (GA), an important building block of biodegradable polymers as well as application in various branches of chemistry, has attracted extensive attention in the industry, while it still encounters challenges of low reaction rate and selectivity. Herein, we reported a cation adsorption strategy to realize the efficient ECH of OX to GA by adsorbing Al3+ ions on an anatase titanium dioxide (TiO2) nanosheet array, achieving 2-fold enhanced GA productivity (1.3 vs 0.65 mmol cm-2 h-1) with higher Faradaic efficiency (FE) (85 vs 69%) at -0.74 V vs RHE. We reveal that the Al3+ adatoms on TiO2 both act as electrophilic adsorption sites to enhance the carbonyl (C═O) adsorption of OX and glyoxylic acid (intermediate) and also promote the generation of reactive hydrogen (H*) on TiO2, thus promoting the reaction rate. This strategy is demonstrated effective for different carboxylic acids. Furthermore, we realized the coproduction of GA at the bipolar of a H-type cell by pairing ECH of OX (at cathode) and electrooxidation of ethylene glycol (at anode), demonstrating an economical manner with maximum electron economy.

Electrocatalytic Upcycling of Biomass and Plastic Wastes to Biodegradable Polymer Monomers and Hydrogen Fuel at High Current Densities.

Transformation of biomass and plastic wastes to value-added chemicals and fuels is considered an upcycling process that is beneficial to resource utilization. Electrocatalysis offers a sustainable approach; however, it remains a huge challenge to increase the current density and deliver market-demanded chemicals with high selectivity. Herein, we demonstrate an electrocatalytic strategy for upcycling glycerol (from biodiesel byproduct) to lactic acid and ethylene glycol (from polyethylene terephthalate waste) to glycolic acid, with both products being as valuable monomers for biodegradable polymer production. By using a nickel hydroxide-supported gold electrocatalyst (Au/Ni(OH)2), we achieve high selectivities of lactic acid and glycolic acid (77 and 91%, respectively) with high current densities at moderate potentials (317.7 mA/cm2 at 0.95 V vs RHE and 326.2 mA/cm2 at 1.15 V vs RHE, respectively). We reveal that glycerol and ethylene glycol can be enriched at the Au/Ni(OH)2 interface through their adjacent hydroxyl groups, substantially increasing local concentrations and thus high current densities. As a proof of concept, we employed a membrane-free flow electrolyzer for upcycling triglyceride and PET bottles, attaining 11.2 g of lactic acid coupled with 9.3 L of H2 and 13.7 g of glycolic acid coupled with 9.4 L of H2, respectively, revealing the potential of coproduction of valuable chemicals and H2 fuel from wastes in a sustainable fashion.

Electrocatalytic synthesis of adipic acid coupled with H2 production enhanced by a ligand modification strategy.

Adipic acid is an important building block of polymers, and is commercially produced by thermo-catalytic oxidation of ketone-alcohol oil (a mixture of cyclohexanol and cyclohexanone). However, this process heavily relies on the use of corrosive nitric acid while releases nitrous oxide as a potent greenhouse gas. Herein, we report an electrocatalytic strategy for the oxidation of cyclohexanone to adipic acid coupled with H2 production over a nickel hydroxide (Ni(OH)2) catalyst modified with sodium dodecyl sulfonate (SDS). The intercalated SDS facilitates the enrichment of immiscible cyclohexanone in aqueous medium, thus achieving 3.6-fold greater productivity of adipic acid and higher faradaic efficiency (FE) compared with pure Ni(OH)2 (93% versus 56%). This strategy is demonstrated effective for a variety of immiscible aldehydes and ketones in aqueous solution. Furthermore, we design a realistic two-electrode flow electrolyzer for electrooxidation of cyclohexanone coupling with H2 production, attaining adipic acid productivity of 4.7 mmol coupled with H2 productivity of 8.0 L at 0.8 A (corresponding to 30 mA cm-2) in 24 h.

Selective Photoelectrocatalytic Glycerol Oxidation to Dihydroxyacetone via Enhanced Middle Hydroxyl Adsorption over a Bi2O3-Incorporated Catalyst.

Photoelectrocatalytic (PEC) glycerol oxidation offers a sustainable approach to produce dihydroxyacetone (DHA) as a valuable chemical, which can find use in cosmetic, pharmaceutical industries, etc. However, it still suffers from the low selectivity (≤60%) that substantially limits the application. Here, we report the PEC oxidation of glycerol to DHA with a selectivity of 75.4% over a heterogeneous photoanode of Bi2O3 nanoparticles on TiO2 nanorod arrays (Bi2O3/TiO2). The selectivity of DHA can be maintained at ∼65% under a relatively high conversion of glycerol (∼50%). The existing p-n junction between Bi2O3 and TiO2 promotes charge transfer and thus guarantees high photocurrent density. Experimental combined with theoretical studies reveal that Bi2O3 prefers to interact with the middle hydroxyl of glycerol that facilitates the selective oxidation of glycerol to DHA. Comprehensive reaction mechanism studies suggest that the reaction follows two parallel pathways, including electrophilic OH* (major) and lattice oxygen (minor) oxidations. Finally, we designed a self-powered PEC system, achieving a DHA productivity of 1.04 mg cm-2 h-1 with >70% selectivity and a H2 productivity of 0.32 mL cm-2 h-1. This work may shed light on the potential of PEC strategy for biomass valorization toward value-added products via PEC anode surface engineering.

Photoelectrocatalytic C-H halogenation over an oxygen vacancy-rich TiO2 photoanode.

Photoelectrochemical cells are emerging as powerful tools for organic synthesis. However, they have rarely been explored for C-H halogenation to produce organic halides of industrial and medicinal importance. Here we report a photoelectrocatalytic strategy for C-H halogenation using an oxygen-vacancy-rich TiO2 photoanode with NaX (X=Cl-, Br-, I-). Under illumination, the photogenerated holes in TiO2 oxidize the halide ions to corresponding radicals or X2, which then react with the substrates to yield organic halides. The PEC C-H halogenation strategy exhibits broad substrate scope, including arenes, heteroarenes, nonpolar cycloalkanes, and aliphatic hydrocarbons. Experimental and theoretical data reveal that the oxygen vacancy on TiO2 facilitates the photo-induced carriers separation efficiency and more importantly, promotes halide ions adsorption with intermediary strength and hence increases the activity. Moreover, we designed a self-powered PEC system and directly utilised seawater as both the electrolyte and chloride ions source, attaining chlorocyclohexane productivity of 412 µmol h-1 coupled with H2 productivity of 9.2 mL h-1, thus achieving a promising way to use solar for upcycling halogen in ocean resource into valuable organic halides.

A quencher-free DNAzyme beacon for fluorescently sensing uranyl ions via embedding 2-aminopurine.

DNAzyme-based fluorescent probes have provided valuable protocols for detecting uranium, one of the most common radioactive contaminants in the environment, with ultra-high selectivity and sensitivity. Designing novel DNAzyme beacons to update the mode of fluorescence reporting and/or quenching will continuously enhance "turn-on" sensing performance as well as promote actual application of the biological probes. In this work, we developed a novel quencher-free DNAzyme beacon by embedding fluorescent 2-aminopurine for rapid detection of uranyl ion. 2-aminopurine is able to substitute adenine and keep strong fluorescence in single-stranded DNA whereas being quenched in the hybridized double-stranded DNA by the base-stacking interaction. The combination of such trait of 2-aminopurine and cleavage reaction of DNAzyme in the presence of target co-factors possesses two main advantages for ion sensing: simplicity for avoidance of extra quencher groups and high performance because of superiority of DNAzyme essence. The experimental conditions including embedding site, pH and salt concentration of buffer solutions, and the amount ratio of enzyme strand to substrate strand used to form DNAzymes were systematically optimized to inspire the highest performance of the biological beacon. Thus, a detection limit of 9.6 nM, a wide linear range from 5 nM to 400 nM (R2 = 0.997), and selectivity of more than 400 000-fold over other metal ions were achieved by the novel DNAzyme probes. The highly sensitive, selective and quencher-free DNAzyme probes accommodated a simple and cost-efficient alternative to current fluorescent counterparts, holding a great potential for further application in practical ion assay.

Metal-Organic Framework [Cd(LTP)2]n for Improved Enantioseparations on a Chiral Cyclodextrin Stationary Phase in GC.

Metal-organic frameworks (MOFs) are a class of novel porous materials consisting of clusters or chains of metal ions and organic linkers. The chiral MOF [Cd(LTP)2]n (LTP = l(-)-thiazolidine-4-carboxylic acid) possesses infinite extension three-dimensional supramolecular reticular structure with right-handed helix. In this work, three capillary columns (A, B and C) containing MOF [Cd(LTP)2]n, permethylated ß-cyclodextrin (CD) and sodium chloride, and MOF [Cd(LTP)2]n and permethylated ß-CD, respectively, have been prepared and their respective enantioseparation abilities have been investigated. The polarities of all of the MOFs and permethylated ß-CDs are moderate. The numbers of theoretical plates (plate m-1) of the three columns have been measured using n-dodecane at 120°C, which followed an increasing order of A (3100) < B (3800) < C (4300). Some racemates were separated with different resolutions on Columns A, B and C. The results indicated that the incorporated MOF [Cd(LTP)2]n enhanced the separations of racemates on a permethylated ß-CD stationary phase with high column efficiency and good reproducibility in gas chromatography.

[Single-handed helical framework material [{Cu(sala)}n] incorporated peramylated ß-cyclodextrin for improving gas chromatography enantioseparation].

Metal-organic frameworks (MOFs) as a new generation of functional molecular materials, have broad application prospects in enantioselective catalysis and chiral separation areas due to their unusual properties, such as high surface area, rich topologies, permanent microporous, availability of outer-surface modification and so on. A single-handed helical three-dimensional metal-organic framework material [{Cu(sala)}n] (H2sala=N-(2-hydroxybenzyl)-L-alanine) was incorporated with peramylated ß-cyclodextrin for the preparation of novel capillary gas chromatography stationary phase. To investigate whether the use of a chiral MOF can enhance enantioseparation on peramylated ß-cyclodextrin, three chiral columns were fabricated using different stationary phases for comparison, including column A ([{Cu (sala)}n]), column B (peramylated ß-cyclodextrin) and column C ([{Cu(sala)}n]+peramylated ß-cyclodextrin). The results of comparing the resolving abilities of the three columns for the same chiral compounds demonstrated that column C showed better enantioselectivity and higher resolution. The use of MOF [{Cu(sala)}n] can improve enantioseparation on peramylated ß-cyclodextrin.