Determination of cysteine via its inhibition of catalytic activity of silver coated ZnO/Fe3O4 composites used for conversion of 4-nitrophenol into 4-aminophenol

PLA/CS-ZnO bionanocomposite for rapid catalytic reduction of nitrophenol compounds as a heterogeneous nanocatalyst

In this research, a high efficiency and environmentally friendly method to reduce nitrophenol compounds such as 4-nitrophenol (4-NP), 2,4,6-trinitrophenol (2,4,6-TNP) and 2,4-dinitrophenol (2,4-DNP) was used in the presence of poly(lactic acid)/chitosan-ZnO ( PLA/CS-ZnO) bionanocomposite. Using FT-IR, SEM, XRD and UV-Vis techniques, PLA/CS-ZnO bionanocomposite was identified after synthesis. Also, the mechanical properties of the bionanocomposite were investigated using the stress-strain curve. The mentioned bionanocomposite showed a very good efficiency in reducing nitrophenol compounds to aminophenolic compounds, so that under optimal conditions, 100% conversion and selectivity in the reduction of 4-NP, 2,4,6-TNP and 2,4-DNP to 4-aminophenol (4-AP), 2,4,6-triaminophenol (2,4,6-TAP) and 2,4-diaminophenol (2,4-DAP) were observed. UV-Vis absorption spectrum at different times were used to evaluate the progress of the reaction. Furthermore, after the reaction, PLA/CS-ZnO was recovered and used for the next cycle. The results showed that the bionanocomposite can perform ten consecutive cycles without a significant decrease in efficiency. The comparison of catalytic activity with other catalysts showed that the bionanocomposite synthesized in the present research has a higher efficiency in reduction of nitrophenol compounds.

Colorimetric detection of chromium (VI) via its instigation of oxidase-mimic activity of CuO

Extensive use of chromium makes it one of the major pollutants of water resources. Chromium (VI) in particular is toxic and has detrimental health effects. Because of its high toxicity a tolerable concentration limit of chromium (VI) in drinking water has been recommended. Here we report a colorimetric method for determination of chromium (VI) in water based on the oxidase-like activity of solvothermal synthesized copper oxide. The particles have been characterized by X- ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). Using 3, 3', 5, 5'- tetramethylbenzidine (TMB) as a chromogenic substrate, CuO exhibited a pronounced oxidase-like activity in the presence of chromium (VI). This method enables successful colorimetric detection of chromium (VI). It demonstrated excellent selectivity for detection of chromium (VI) ions against potentially interfering ions. The method's feasibility to real sample analysis has been proven by testing tap water. Hence, we anticipate that the method can be successfully applied for analysis of chromium (VI) in environmental samples.

A comparative study of Cu-anchored 0D and 1D ZnO nanostructures for the reduction of organic pollutants in water

In this work, Cu NPs were loaded at a fixed percentage (5 wt%) on 1D, (1D + 0D) and 0D ZnO nanostructures to investigate the effect of the support morphology on the reduction of organic pollutants in water. The synthesized materials were characterized by high-resolution transmission electron microscopy (HR-TEM), ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), N2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS). The results reveal that the loading of Cu NPs decreases the optical band gap, and a slight change in the crystallite sizes increases the specific surface area value of the nanocomposites. The TEM images reveal that 1D ZnO has an average width of 44.7 nm and an average length of 211 nm, while 0D ZnO has an average diameter of 54.5 nm. The HR-TEM and XPS data confirm the loading of metallic Cu NPs on the surface of the ZnO nanostructures. The pure ZnO and nanocomposites were tested for 4-nitrophenol (4-NP) reduction in the presence of NaBH4 at room temperature. The obtained results show that pure ZnO nanostructures have no catalytic performance, while the nanocomposites showed good catalytic activities. The catalytic reduction efficiency of 4-NP was found to follow the order of Cu/0DZnO > Cu/(1D + 0D)ZnO > Cu/1DZnO. The complete reduction of 4-NP has been observed to be achievable within 60 s using the Cu/0DZnO nanocomposite, with a k app value of 8.42 min-1 and good recyclability of up to five cycles. This nanocomposite was then applied in the reduction of organic dyes in water; it was found that the reduction rate constants for the methylene blue, Congo red, and acriflavine hydrochloride dyes were 1.4 min-1, 1.2 min-1, and 3.81 min-1, respectively. The high catalytic performance of this nanocomposite may be due to the small particle size, high specific surface area, and the high dispersion of Cu NPs on the surface of ZnO.

High-Sensitivity Enzymatic Glucose Sensor Based on ZnO Urchin-like Nanostructure Modified with Fe3O4 Magnetic Particles

A novel and efficient enzymatic glucose sensor was fabricated based on Fe₃O₄ magnetic nanoparticles (Fe₃O₄MNPs)-modified urchin-like ZnO nanoflowers (ZnONFs). ZnONFs were hydrothermally synthesizing on a flexible PET substrate. Fe₃O₄MNPs were deposited on the surface of the ZnONFs by the drop-coating process. The results showed that the urchin-like ZnONFs provided strong support for enzyme adsorption. For Fe₃O₄MNPs, it significantly promoted the redox electron transfer from the active center of GOx to the ZnO nanoflowers beneath. More importantly, it promoted the hydrolysis of H₂O₂, the intermediate product of glucose catalytic reaction, and thus improved the electron yield. The sensitivity of the Nafion/GOx/Fe₃O₄MNPs/ZnONFs/Au/PET sensor was up to 4.52 μA·mM^-1·cm^-2, which was improved by 7.93 times more than the Nafion/GOx/ZnONFs/Au/PET sensors (0.57 μA·mM^-1·cm^-2). The detection limit and linear range were also improved. Additionally, the as-fabricated glucose sensors show strong anti-interference performance in the test environment containing organic compounds (such as urea, uric acid, and ascorbic acid) and inorganic salt (for instance, NaCl and KCl). The glucose sensor's service life was evaluated, and it can still maintain about 80% detection performance when it was reused about 20 times. Compared with other existing sensors, the as-fabricated glucose sensor exhibits an ultrahigh sensitivity and wide detection range. In addition, the introduction of Fe₃O₄MNPs optimized the catalytic efficiency from the perspective of the reaction mechanism and provided potential ideas for improving the performance of other enzymatic biosensors.

A study on the high efficiency reduction of p-nitrophenol (4-NP) by a Fe(OH)3/Fe2O3@Au composite catalyst

Precious metal nanometric catalysts are widely used in the removal of harmful substances. In the process of synthesis and catalytic reaction, it is particularly important to study green and simple synthesis methods and high catalytic efficiency. In this paper, a green one-step method was used to synthesize the Fe(OH)₃/Fe₂O₃@Au composite catalyst, in which Au was single atom-dispersed. The removal of 4-nitrophenol (4-NP), a typical dangerous chemical widely existing in factory waste gas, waste water and automobile exhaust gas, was catalysed by Fe(OH)₃/Fe₂O₃@Au. The catalytic performance of Fe(OH)₃/Fe₂O₃@Au with different synthesis conditions (different amounts of MES, NaBH₄, FeSO₄, Au and Pt) on the 4-NP reduction reaction were systematically studied. Finally, the stability and recyclability of Fe(OH)₃/Fe₂O₃@Au composite nanocatalyst were investigated thoroughly.