Cobalt-Nanoparticles-Decorated 3D Porous Nitrogen-Doped Carbon Network for Electrocatalytic Nitrite Reduction to Ammonia.

Electrocatalytic nitrite (NO2-) reduction offers the potential to synthesize high-value ammonia (NH3) while simultaneously removing NO2- pollution from aqueous solutions, but it requires high-efficiency catalysts to drive the complex six-electron reaction. Herein, cobalt-nanoparticle-decorated 3D porous nitrogen-doped carbon network (Co@NC) is proven as a high-efficiency catalyst for the selective electroreduction of NO2- to NH3. Such Co@NC attains a large NH3 yield of 922.7 µmol h-1 cm-2 and a high Faradaic efficiency of 95.4% under alkaline conditions. Furthermore, it shows remarkable electrochemical stability during cyclic electrolysis.

A Hierarchical CuO Nanowire@CoFe-Layered Double Hydroxide Nanosheet Array as a High-Efficiency Seawater Oxidation Electrocatalyst.

Seawater electrolysis has great potential to generate clean hydrogen energy, but it is a formidable challenge. In this study, we report CoFe-LDH nanosheet uniformly decorated on a CuO nanowire array on Cu foam (CuO@CoFe-LDH/CF) for seawater oxidation. Such CuO@CoFe-LDH/CF exhibits high oxygen evolution reaction electrocatalytic activity, demanding only an overpotential of 336 mV to generate a current density of 100 mA cm-2 in alkaline seawater. Moreover, it can operate continuously for at least 50 h without obvious activity attenuation.

Adsorption of Pb(II) from water by treatment with an O-hydroxyphenyl thiourea-modified chitosan.

An O-hydroxyphenyl thiourea-modified chitosan (OTCS) with excellent Pb(II) adsorption performance and selectivity was prepared as an adsorbent. The structure and morphology of the adsorbent were systematically investigated by SEM, BET, FTIR, EDX, zeta-potential measurements, XPS and XRD. The impacts of the initial Pb(II) concentration, reaction time, temperature, pH value, and coexisting ions were explored. At pH 7 and 303 K, the maximal adsorption capacity of OTCS for Pb(II) was 208.33 mg/g, which was greater than those of other adsorbing materials reported in the literature. The metal ion adsorption kinetics and isotherm models were found to obey pseudo-second-order kinetics and the Langmuir isothermal model, indicating that the adsorption process was monolayer chemisorption. The adsorption process could proceed spontaneously, and the thermodynamic results revealed that the adsorption mechanism was an endothermic reaction. The ion exchange and chelation between the sulfur, nitrogen and oxygen groups on the adsorbent and lead ions endowed the material with excellent adsorption properties. Significantly, OTCS showed excellent selectivity toward Pb(II). Therefore, the adsorbent OTCS is expected to promote the wider application of chitosan in the adsorption of Pb(II).

Selective removal of Au(III) from wastewater by pyridine-modified chitosan.

A pyridine-modified chitosan (PMCS) adsorbent with excellent adsorption performance and specific selectivity for Au(III) in wastewater was prepared. FTIR, SEM, XPS and XRD were used to study its adsorption performance, and various models were used to fit and analyze the experimental adsorption data. The maximum adsorption capacity of PMCS for Au(III) is 549.41 mg/g (298 K, pH = 4). The data analysis results prove that the PSO and Langmuir models best describe the adsorption process. Adsorption experiments in the presence of multiple ions proved that PMCS is selective for the adsorption of Au(III). The adsorption and desorption experiments showed that the adsorption rate of PMCS could still reach 94.77% after three cycles. In summary, PMCS was demonstrated to be a high-quality material for the adsorption of Au(III) from wastewater due to its excellent adsorption performance, specific selectivity and reusability.

A novel benzothiazole modified chitosan with excellent adsorption capacity for Au(III) in aqueous solutions.

A novel benzothiazole modified chitosan (BCS) with excellent Au(III) adsorption performance and selectivity was prepared as adsorbents. The structure and morphology of the adsorbents were characterized by FTIR, SEM, XRD and XPS. The adsorption property of the adsorbents for Au(III) were investigated under different reaction time, initial concentration of Au(III), temperature, pH and coexisting ions. The maximum adsorption capacity of BCS for Au(III) was 1072.22 mg/g at 298 K and optimal pH = 4, which was better than that of other adsorbents reported in literature. The adsorption kinetics and isotherm models fit the pseudo-second-order and Langmuir equations. This shows that the adsorption process of Au(III) is a monolayer chemical adsorption. The adsorption process can proceed spontaneously and belong to the endothermic reaction according to the thermodynamic results. The excellent adsorption performance is mainly attributed to the ion exchange and chelation of the nitrogen, sulfur and oxygen groups on the adsorbent with gold ions. Significantly, BCS has excellent selectivity toward Au(III) and remarkable recycle performance. With the high adsorption capacity, excellent selectivity and outstanding reusability, the BCS adsorbent could be a promising candidate to adsorb Au(III) from wastewater.

Multiple roles of dissolved organic matter released from decomposing rice straw at different times in organic pollutant photodegradation.

Rice straw returning causes a considerable amount of dissolved organic matter (DOM) release into aquatic croplands in a relatively short-term. The presence of rice straw-derived DOM in cropland waters may alter the photochemical behaviors of organic pollutants. However, the photochemical activity and photosensitization role of the DOMs are poorly understood. Here, eight DOM samples were extracted from decomposing rice straw at different times in 49 days to explore their photosensitizing capacities toward diuron (DIU), 17ß-estradiol (E2), and sulfamethoxazole (SMX). All of the DOMs were photosensitive and mainly composed of tryptophan-, tyrosine- and fulvic-like substances. Over the decomposition period, the amount of photochemically produced reactive intermediates (PPRIs) by the DOMs peaked on days 7 and 14. The evolution of the DOM photosensitizing capacity towards DIU and E2 was consistent with the variations of PPRIs, and HO· was confirmed as a critical factor. However, the influence of the DOMs on SMX photodegradation was opposite to that on DIU and E2. The positive role of the DOMs in SMX photodegradation was attributed to the tryptophan-like components. The results suggest that straw-derived DOM is an important photosensitizer and that its photosensitization towards organic pollutants is dependent on straw decomposing time and pollutant type.

Predictive role of spectral slope ratio towards 17α-ethynylestradiol photodegradation sensitized by humic acids.

Humic acids (HAs) have been shown to dominate the photodegradation of steroid estrogens in natural waters. Nevertheless, how the photosensitizing ability of HAs relates to their structural and optical characteristics remains largely unknown. In this study, 17α-ethynylestradiol (EE2) was selected as a model compound to study to what extent easily-measurable characteristics of HAs might be used to predict their photosensitization potency. HAs were extracted from sediments of two different sources, and then subjected to structural and optical properties characterization using elemental analyzer, UV-vis spectroscopy and fluorescence spectroscopy. Photochemical experiments show that the HAs from the two sources can effectively meditate EE2 photodegradation. Although with drastically different structural and optical properties, the photosensitizing ability of these HAs towards EE2 can be well described by simple linear regressions using a spectroscopic index, the spectral slope ratio (SR). This optical indicator is correlated with various physicochemical properties of HAs, including the molecular weight, lignin content, charge-transfer interaction potential, photobleaching extent and sources. No universal prediction model could be established for predicting EE2 photodegradation kinetics on the basis of SR, but in specific waters SR could be a powerful indictor for predicting the EE2 photodegradation sensitized by HAs.