Waste remediation: Low-temperature synthesis of hybrid Cu(OH)2/CuO and CuO nanostructures from spent printed circuit boards and their dye degradation studies

The demand for environmentally friendly and sustainable resource utilization techniques for recycling waste printed circuit boards is significant due to their status as valuable secondary resources, containing high-purity copper and precious metals. In this context, Cu(OH)2/CuO and CuO nanostructures were fabricated using alkaline precipitation and low-temperature aging methods using the strip solution originated from laboratory-scale spent mobile phone printed circuit board recovery process. XRD, FTIR, FESEM-EDX, and TEM were utilized to characterize the as-recovered nanoproducts. A hybrid structure of Cu(OH)2/CuO was formed at 70°, and monoclinic CuO phase was formed at 80 °C aging time. The results show that Cu(OH)2/CuO nanoflakes have an average crystallite size of 24.06 nm and a particle width of 22 ± 3 nm. Cu(OH)2/CuO nanoflakes formed at 70 °C aging temperature and 24-h residence time have finer crystallite and particle sizes than CuO-ridged nanospheres formed at 80 °C aging temperature. The optical band gap energy of Cu(OH)2/CuO and CuO nanostructures formed was found to be 2.28 eV and 2.22 eV, respectively. The hybrid Cu(OH)2/CuO nanostructure photocatalyzed the decomposed 97.28% rhodamine blue using a visible light source, whereas the CuO nanostructure degraded only 14.64% rhodamine blue dye under similar conditions. A surfactant-less hybrid structure is developed without the use of any chemical precursor. Thus, a high value-added product is produced using one waste material to remove another waste in wastewater treatment.

Efficient and Selective Electrochemical Nitrate Reduction to N2 Using a Flow-Through Zero-Gap Electrochemical Reactor with a Reconstructed Cu(OH)2 Cathode: Insights into the Importance of Inter-Electrode Distance

Electrochemically converting nitrate, a widely distributed nitrogen contaminant, into harmless N2 is a feasible and environmentally friendly route to close the anthropogenic nitrogen-based cycle. However, it is currently hindered by sluggish kinetics and low N2 selectivity, as well as scarce attention to reactor configuration. Here, we report a flow-through zero-gap electrochemical reactor that shows a high performance of nitrate reduction with 100% conversion and 80.36% selectivity of desired N2 in the chlorine-free system at 100 mg-N·L-1 NO3- while maintaining a rapid reduction kinetics of 0.07676 min-1. More importantly, the mass transport and current utilization efficiency are significantly improved by shortening the inter-electrode distance, especially in the zero-gap electrocatalytic system where the current efficiency reached 50.15% at 5 mA·cm-2. Detailed characterizations demonstrated that during the electroreduction process, partial Cu(OH)2 on the cathode surface was reconstructed into stable Cu/Cu2O as the active phase for efficient nitrate reduction. In situ characterizations revealed that the highly selective *NO to *N conversion and the N-N coupling step played crucial roles during the selective reduction of NO3- to N2 in the zero-gap electrochemical system. In addition, theoretical calculations demonstrated that improving the key intermediate *N coverage could effectively facilitate the N-N coupling step, thereby promoting N2 selectivity. Moreover, the environmental and economic benefits and long-term stability shown by the treatment of real nitrate-containing wastewater make our proposed electrocatalytic system more attractive for practical applications.

Novel Ta/chitosan-doped CuO nanorods for catalytic purification of industrial wastewater and antimicrobial applications

Novel tantalum (Ta) and chitosan (CS)-doped CuO nanorods (NRs) were synthesized using a single step co-precipitation route. Different concentrations (2 and 4%) of Ta were used in fixed amounts of CS and CuO to examine their catalytic activity and antimicrobial potential. For critical analysis, synthesized NRs were systematically examined using XRD, FTIR HRTEM, EDS, UV-Vis and PL spectroscopy. The XRD technique revealed the monoclinic structure of CuO while an increase in its crystallite size (from 15.5 to 18.5 nm) was observed upon doping. FTIR spectra were examined to study the functional groups of CuO where peaks at 514 cm-1 and 603 cm-1 confirmed the formation of CuO NRs. PL spectra depicted the charge transfer efficiency of the synthesized samples. The presence of dopants (Ta and CS) and constituent elements (Cu, O) was detected using EDS spectra. Additionally, the pH based catalytic performance of fabricated NRs revealed 99.7% dye degradation of toxic methylene blue (MB) dye in neutral media, 99.4% in basic media and 99.5% in acidic media along with promising antibacterial activities for Gram negative/positive bacteria, respectively upon doping of Ta (4%) into CS/CuO. The adsorption energies of CuO co-doped with CS/Ta led to the creation of stable structures that were investigated theoretically using density functional theory.

Highly Efficient Industrial Dye Degradation, Bactericidal Properties, and In Silico Molecular Docking Analysis of Ag/Cellulose-Doped CuO Nanostructures

In this research, CuO nanostructures doped with Ag and cellulose nanocrystals (CNC) were synthesized using a facile coprecipitation technique. In this work, we doped Ag into fixed quantities of CNC and CuO to improve the photocatalytic, catalytic, and antibacterial activity. It was noted that catalytic activity increased upon doping, which was attributed to the formation of nanorods and a pH effect, while the reverse trend was observed in photocatalytic activity. The addition of Ag and CNC dopants into CuO improved the bactericidal efficacy for S. aureus and E. coli. In addition, to obtain insight into the possible mechanism behind their biocidal effects, molecular docking studies were conducted against specific enzyme targets: namely, dihydrofolate reductase from E. coli and DNA gyrase from S. aureus. This study suggested that codoped CuO could be highly efficient in the cleaning of polluted water and antibacterial applications.

Synthesis of one dimensional Cu2S nanorods using a self-grown sacrificial template for the electrocatalytic oxygen evolution reaction (OER)

The oxygen evolution reaction (OER) is critical in electrochemical water splitting and requires an efficient, sustainable, and cheap catalyst for successful practical applications.

Gold Nanoparticles Supported on Urchin-Like CuO: Synthesis, Characterization, and Their Catalytic Performance for CO Oxidation

Gold catalysts have been studied in-depth due to their unique activities for catalytic CO oxidation. Supports have intrinsic motivation for the high activity of gold catalysts. Thermally stable urchin-like CuO microspheres, which are potential support for gold catalysts, were prepared by facile solution-method. Then gold nanoparticles were loaded on them by deposition-precipitation method. The obtained gold catalysts were characterized by SEM, XRD, TEM, BET, ICP, and XPS. Their catalytic activity for CO oxidation was also evaluated. TEM results revealed that the gold nanoparticles with small sizes were highly distributed on the CuO surface in Au_1.0/CuO-300. XPS observations demonstrated that the gold species in Au_1.0/CuO-300 was of metallic state. Among the as-prepared catalysts, the Au_1.0/CuO-300 catalyst displayed the best performance for CO oxidation and achieved 100% CO oxidation at 80 °C. It kept 100% conversion for 20 h at a reaction temperature of 180 °C, and showed good reusability after three reaction-cycles. The possible catalytic mechanism of Au_1.0/CuO-300 catalyst for CO oxidation was also briefly proposed.

Nanoscale modification of one-dimensional single-crystalline cuprous oxide

In this work we report for the first time a method to modify the surface of Cu₂O nanowires in a controllable way and physically weld them into a network form, which contributes to higher electrical conductivity as well as a strong water-repelling nature. We have used state-of-the-art theoretical calculations to support our experimental observations. We demonstrate how varying the irradiation fluence can modulate the surface and decorate the nanowire with a uniform distribution of Cu₈O nanocrystals due to preferential sputtering. While several well studied joining techniques are available for carbon and metal-based nanowires, the same information for ceramic nanowires is scarce at present. The current study sheds light into this and a state-of-the-art 3D simulation technique predicts most of the modifications including surface modulation, oxygen depletion and welding. The welded network shows higher electrical conductivity than the unwelded assembly. With Cu₂O being of p-type the current ion beam joining technique shows a novel path for fabricating p-i-n junctions or solar cell devices through bottom-up approach. Furthermore, we have explored the response of this network to moisture. Our calculation based on density functional theory predicts the hydrophilic nature of individual copper oxide nanowires both before and after irradiation. However, the network shows a strong water-repelling nature, which has been explained quantitatively using the Cassie-Baxter model.

Photocatalytic activity of CuO/Cu(OH)2 nanostructures in the degradation of Reactive Green 19A and textile effluent, phytotoxicity studies and their biogenic properties (antibacterial and anticancer)

In this study, CuO/Cu(OH)₂ (denoted as CuONs) nanostructures were synthesized relying to a cheap and rapid chemical co-precipitation method using copper sulfate and liquid ammonia as precursors. Results obtained from X-ray diffraction, and field emission scanning electron microscopy analysis revealed the crystalline nature of synthesized CuONs. Fourier transform infrared spectroscopy and energy dispersive spectroscopy studies showed interactions between copper and oxygen atoms. Synthesized CuONs showed the size in the range of 20-30 nm using high resolution transmission electron microscopy analysis. The photocatalytic degradation performance of Reactive Green 19A (RG19A) dye using CuONs was evaluated. The results showed that CuONs exhibited 98% degradation efficiency after 12 h and also complete mineralization in form of reducing chemical oxygen demand (COD) (84%) and total organic carbon (TOC) (80%). The nanocatalyst was recovered from the dye containing solution and its catalytic activity can be reused up to four times efficiently. CuONs was also able to decolorize actual textile effluent (80% in terms of the American Dye Manufacturers' Institute (ADMI) value) with significant reductions in COD (72%) and TOC (69%). Phytotoxicity studies revealed that the degradation products of RG19A and textile effluent were scarcely toxic in nature, thereby increasing the applicability of CuONs for the treatment of textile wastewater. Additionally, the CuONs showed a maximum antibacterial effect against human pathogens which also displayed synergistic antibacterial potential related to commercial antibiotics. Moreover, CuONs displayed strong antioxidant activity in terms of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (IC₅₀: 51 μg/mL) and DPPH (1,1-diphenyl-2-picrylhydrazyl) (IC₅₀: 60 μg/mL) radical scavenging. The CuONs exhibited dose dependent response against tumor rat C6 cell line (IC₅₀: 60 μg/mL) and may serve as anticancer agents.

Facile synthesis of 3D flower-like Cu2−xSe nanostructures via a sacrificing template method and their excellent antibacterial activities

The flower-like Cu_2−xSe assembled from hexagonal nanosheets shows excellent antibacterial activities to S. aureus and E. coli, and its antibacterial mechanism was confirmed experimentally.

Studies on structural defects in bare, PVP capped and TPPO capped copper oxide nanoparticles by positron annihilation lifetime spectroscopy and their impact on photocatalytic degradation of rhodamine B

Enhanced photocatalytic dye degradation by reducing sizes of surface defects.