Exploring Copper Oxide and Copper Sulfide for Non-Enzymatic Glucose Sensors: Current Progress and Future Directions

Millions of people worldwide are affected by diabetes, a chronic disease that continuously grows due to abnormal glucose concentration levels present in the blood. Monitoring blood glucose concentrations is therefore an essential diabetes indicator to aid in the management of the disease. Enzymatic electrochemical glucose sensors presently account for the bulk of glucose sensors on the market. However, their disadvantages are that they are expensive and dependent on environmental conditions, hence affecting their performance and sensitivity. To meet the increasing demand, non-enzymatic glucose sensors based on chemically modified electrodes for the direct electrocatalytic oxidation of glucose are a good alternative to the costly enzymatic-based sensors currently on the market, and the research thereof continues to grow. Nanotechnology-based biosensors have been explored for their electronic and mechanical properties, resulting in enhanced biological signaling through the direct oxidation of glucose. Copper oxide and copper sulfide exhibit attractive attributes for sensor applications, due to their non-toxic nature, abundance, and unique properties. Thus, in this review, copper oxide and copper sulfide-based materials are evaluated based on their chemical structure, morphology, and fast electron mobility as suitable electrode materials for non-enzymatic glucose sensors. The review highlights the present challenges of non-enzymatic glucose sensors that have limited their deployment into the market.

Developing Benign Ni/g-C3N4 Catalysts for CO2 Hydrogenation: Activity and Toxicity Study

This research discusses the CO2 valorization via hydrogenation over the non-noble metal clusters of Ni and Cu supported on graphitic carbon nitride (g-C3N4). The Ni and Cu catalysts were characterized by conventional techniques including XRD, AFM, ATR, Raman imaging, and TPR and were tested via the hydrogenation of CO2 at 1 bar. The transition-metal-based catalyst designed with atom-economy principles presents stable activity and good conversions for the studied processes. At 1 bar, the rise in operating temperature during CO2 hydrogenation increases the CO2 conversion and the selectivity for CO and decreases the selectivity for methanol on Cu/CN catalysts. For the Ni/CN catalyst, the selectivity to light hydrocarbons, such as CH4, also increased with rising temperature. At 623 K, the conversion attained ca. 20%, with CH4 being the primary product of the reaction (CH4 yield >80%). Above 700 K, the Ni/CN activity increases, reaching almost equilibrium values, although the Ni loading in Ni/CN is lower by more than 90% compared to the reference NiREF catalyst. The presented data offer a better understanding of the effect of the transition metals' small metal cluster and their coordination and stabilization within g-C3N4, contributing to the rational hybrid catalyst design with a less-toxic impact on the environment and health. Bare g-C3N4 is shown as a good support candidate for atom-economy-designed catalysts for hydrogenation application. In addition, cytotoxicity to the keratinocyte human HaCaT cell line revealed that low concentrations of catalysts particles (to 6.25 μg mL-1) did not cause degenerative changes.

The confinement effects of ordered mesoporous carbon on copper nanoparticles for methanol oxidative carbonylation

The confinement of Cu nanoparticles in narrow mesopores strengthens the Cu–carbon interactions. This can promote the auto-reduction of CuO to form active Cu2O species, resulting in high activity and stability during DMC synthesis.

CoZn-ZIF-derived carbon-supported Cu catalyst for methanol oxidative carbonylation to dimethyl carbonate

Carbon materials derived from CoZn-ZIFs were used to load Cu catalysts and were applied for DMC synthesis, and the effects of the graphitization degree and the (N1 + N3)/N2 ratio were studied.

Bio-carbon-layered CuO-catalyzed decarboxylative alkenylation of cyclic ethers

An efficient methodology for the direct decarboxylative functionalization of cinnamic acid derivatives with cyclic ethers has been developed by using biogenic CuO/C nanoparticles. This protocol is compatible with broad range of substrates.

Genesis and Properties of MOx/CNTs (M = Ce, Cu, Mo) Catalysts for Aerobic Oxidative Desulfurization of a Model Diesel Fuel

Aerobic oxidative desulfurization of a model diesel fuel over MOx/CNTs catalysts (M = Ce, Cu, Mo) was studied to develop innovative technology for cleaning motor fuels to EURO-5 standard. It was shown that the thermal stability of catalysts improves in the following order of metal Сu < Сe < Мо. The disordering of the carbon matrix of support increases in the next row of M: Mo < Ce < Cu, which is accompanied by an increase in the specific surface area of the samples (40 → 105 m2/g). The forms of stabilization of the active component (CeO2, CuO/Cu2O/ Cu, or MoO3/MoO2) were revealed, indicating a partial reduction of the metal cations during the thermal decomposition of copper and molybdenum precursor compounds deposited on CNTs. In oxidative desulfurization of a model diesel fuel over MOx/CNTs catalysts at 150 °C the total conversion of dibenzothiophene increased in the next row of M: Се < Сu < Мо. It was found that at 150 °C over the optimum MoOx/CNTs catalyst the highest dibenzothiophene conversion 95–99% is observed. It was assumed that the high activity of MoOx/CNTs is associated with both the oxidizing ability and the tendency of MoOx to chemosorption of sulfur compounds.

In Situ Preparation of Copper-Loaded Carbon-Based Catalyst with Chelate Resin and Its Application on Persulfate Activation for X-3B Degradation

Under the guidance of the idea of “treating waste with waste”, copper-loaded carbon-based catalysts were prepared in situ using waste chelating resin with adsorbed copper. The effect of the catalyst activation temperature on dye brilliant red (X-3B) degradation was investigated and the characterization of the catalysts was analyzed. The results show that a catalyst activated at 800 °C (Cu-AC-800) has the largest specific surface area and abundant pore structure and the highest proportion of Cu under low valence states, which leads to the best performance in adsorbing and degrading X-3B. The influences of operation conditions and inorganic salt anions on persulfate (PS) activation were also investigated. Moreover, the degradation mechanism was preliminarily explored by quenching reactions. The main active free radicals in the system were determined as sulfate radicals (•SO4−). Given its use in solid waste recycling, copper-loaded carbon-based catalyst may provide some new insights for the remediation of wastewater.