We report the hydroxide (OHad) and oxide (Oad) experimental electroadsorption free energies, their dependences on pH, and their correlations to the oxygen evolution reaction (OER) electrocatalysis on ...RuO2(110) surface. The Sabatier principle predicts that catalyst is most active when the intermediate stabilization is moderate, not too strong such that the bound intermediate disrupts the subsequent catalytic cycle, nor too weak such that the surface is ineffective. For decades, researchers have used this concept to rationalize the activity trend of many OER electrocatalysts including RuO2, which is among the state-of-the-art OER catalysts. In this article, we report an experimental assessment of the Sabatier principle by comparing the oxygen electroadsorption energy to the OER electrocatalysis for the first time on RuO2. We find that the OHad and Oad electroadsorption energies on RuO2(110) depend on pH and obey the scaling relation. However, we did not observe a direct correlation between the OHad and Oad electroadsorption energies and the OER activity in the comparative analysis that includes both RuO2(110) and IrO2(110). Our result raises a question of whether the Sabatier principle can describe highly active electrocatalysts, where the kinetic aspects may influence the electrocatalysis more strongly than the electroadsorption energy, which captures only the thermodynamics of the intermediates and not yet kinetics.
Unorthodox luminogenic polymers without aromatic luminogens have attracted great interest in recent years; however, the low fluorescence efficiency is still a big drawback. In this paper, we ...synthesized a fluorescent hyperbranched polysiloxane with both carbonyl and vinyl groups (P1). Surprisingly, it exhibited nontraditional intrinsic luminescence with the highest quantum yield up to 43.9% among the reported silica-containing hyperbranched fluorescent polymers to date. Reference oligomers P2 and P3, theoretical calculations, and transmission electron microscopy were employed to explore the fluorescence mechanism. The high fluorescence quantum yield is ascribed to the synergism of vinyl and carbonyl groups as well as the Si–O group-promoted through-space conjugation. Thus, the supramolecular hyperbranched polysiloxane was assembled by conjugation to increase the oscillator strength and decrease the band gap. Moreover, the solvent effect and pH dependency properties of P1 and its application as an Fe3+ probe were also studied.
•The lignin of corncob-based biochar can be grafted by acrylonitrile.•The modified biochar showed extraordinary Cd adsorption capacity.•The Cd removal mechanism is ion exchange and ...adsorption-complexation.•A new method to recycle agricultural waste.
In order to improve the adsorption capacities of corncob-based biochars for heavy metal, the different pyrolysis temperature (350 °C, 450 °C and 550 °C) of corncob-based biochars were modified with the acrylonitrile, and adsorption capacities of Cadmium from solution by biochars were studied. The results showed that only at 350 °C the biochar can be successfully modified. The Cd adsorption capacity (85.65 mg/g) by the biosorbent was higher than other methods of modifying biochars previously reported. SEM-EDS and FTIR confirmed that the CN group was grafted on the biochar at low pyrolysis temperature. Batch adsorption experiment including pH-dependence, adsorption kinetics, and isotherms and XPS results showed that the removal mechanism of Cd(II) by the modified biochar was ion exchange and adsorption-complexation. This research not only obtained a novel method to modify biochar but also furthered research into the lignin of biochar composition, and provided an efficient sorbent for heavy metal.
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•Increasing pH facilitated the degradation of TTC.•Seven intermediates of TTC were identified by SPE–LC–MS/MS.•TTC was transferred via N-demethylation, hydroxylation–oxidation and ...dehydration.•Degradation of TCs followed the order of OTC>CTC>TTC.•TTC was degraded much faster in artificial surface water.
Tetracyclines (TCs), including tetracycline (TTC), oxytetracycline (OTC), and chlorotetracycline (CTC), are frequently detected in natural waters, soils, and sediments, which raised great concerns about the proliferation of antibiotic resistant genes. This study investigated the degradation of TCs by sulfate radical produced by thermo-activated persulfate in aqueous solution. Increasing the temperature significantly enhanced the degradation of TTC, and the relationship between pseudo-first-order rate constant (kobs) and temperature obeyed Arrhenius equation. The degradation of TTC showed pH dependence, and kobs increased markedly with increasing pH. Seven intermediate products of TTC were temporarily identified by solid phase extraction and liquid chromatography–tandem mass spectrometry (SPE–LC–MS/MS). The transformation pathways of TTC included N-demethylation, hydroxylation–oxidation and dehydration. Detailed mechanisms for sulfate radical-induced N-demethylation and hydroxylation–oxidation were proposed. The degradation of the three TCs followed the order of OTC>CTC>TTC, highlighting the structure-specific reactivity. Interestingly, TTC was degraded extremely fast in artificial surface water (ASW), implying sulfate radical-based oxidation of TCs may be efficient in environmentally relevant conditions. The antimicrobial potency and ecotoxicological effects of the degradation products warrant further studies.
•We show the advantage of the RHE reference in pH partial reaction order studies.•We discuss possible pH-dependent reaction steps for the oxygen evolution reaction.•A method to convert reaction ...orders from SHE to RHE reference is provided.•The reaction order with respect to RHE is measured for RuO2.•Dependencies of RHE reaction order on material properties are analyzed.
Understanding the mechanism of the oxygen evolution reaction (OER) is essential to develop better electrocatalysts for solar fuel generation. Measuring the pH dependence of the OER activity can provide insights on the reaction path that are otherwise difficult to access experimentally, in particular on the coupling of protons and electrons during the reaction. We argue that the use of a pH-dependent reference electrode, such as the reversible hydrogen electrode, is more suitable for these studies as it assures that the overpotential is fixed while varying the pH. We provide criteria for pH dependence when this reference is used and validate the existing results with our measurements on RuO2 powders. A statistical analysis of the existing results allows us to sketch trends in the reaction order on pH with respect to the number of d electrons, oxidation states, and crystal families, providing the groundwork for future OER mechanistic studies on oxides.
Biochars have demonstrated great potential for water decontamination and soil remediation; however, their redox reactivity toward trace contaminants and the corresponding redox-active moieties (RAMs, ...i.e., phenolic −OH, semiquinone-type persistent free radicals (PFRs), and quinoid CO) remain poorly understood. Here we investigated the roles of the RAMs on biochar in oxidation of As(III) under varying pH and O2 conditions. The results showed that the promoted oxidation of As(III) by the RAMs is strongly pH dependent. Under acidic and neutral conditions, only the oxidation of As(III) by •OH and H2O2 produced from activation of O2 by phenolic −OH and semiquinone-type PFRs occurred. In contrast, the oxidation by semiquinone-type PFRs, quinoid CO, and H2O2 (if O2 was introduced) appeared under alkaline conditions. This pH-dependent oxidation behavior was attributed to the varying redox activities of RAMs, as confirmed by multiple characterization and validation experiments using biochar with tuned RAMs compositions, as well as thermodynamics evaluation. Our findings provide new insights into the roles of the RAMs on biochar in the promoted oxidation of trace As(III) over a broader pH range under both anoxic and oxic conditions. This study also paves a promising way to oxidize As(III) with biochar.
Driven by the persisting poor understanding of the sluggish kinetics of the hydrogen evolution reaction (HER) on Pt in alkaline media, a direct correlation of the interfacial water structure and ...activity is still yet to be established. Herein, using Pt and Pt–Ni nanoparticles we first demonstrate a strong dependence of the proton donor structure on the HER activity and pH. The structure of the first layer changes from the proton acceptors to the donors with increasing pH. In the base, the reactivity of the interfacial water varied its structure, and the activation energies of water dissociation increased in the sequence: the dangling O−H bonds < the trihedrally coordinated water < the tetrahedrally coordinated water. Moreover, optimizing the adsorption of H and OH intermediates can re‐orientate the interfacial water molecules with their H atoms pointing towards the electrode surface, thereby enhancing the kinetics of HER. Our results clarified the dynamic role of the water structure at the electrode–electrolyte interface during HER and the design of highly efficient HER catalysts.
On nickel–platinum alloy nanoparticles under alkaline conditions, the reactivity of interfacial water varies with its structure and the order of water dissociation. The inclusion of nickel re‐orientates interfacial water molecules with their hydrogen atoms pointing towards the electrode surface, thereby enhancing the kinetics of the hydrogen evolution reaction (HER).
The successful deployment of advanced energy‐conversion systems depends critically on our understanding of the fundamental interactions of the key adsorbed intermediates (hydrogen *H and hydroxyl ...*OH) at electrified metal–aqueous electrolyte interfaces. The effect of alkali metal cations (Li+, Na+, K+, Cs+) on the non‐Nernstian pH shift of the step‐related voltammetric peak of the Pt(553) electrode is investigated over a wide pH window (1 to 13) by means of experimental and computational methods. The co‐adsorbed alkali cations along the step weaken the OH adsorption at the step sites, causing a positive shift of the potential of the step‐related peak on Pt(553). Density functional calculations explain the observations on the identity and concentration of alkali cations on the non‐Nernstian pH shift, and demonstrate that cation–hydroxyl co‐adsorption causes the apparent pH dependence of “hydrogen” adsorption in the step sites of platinum electrodes.
Keeping in step: A combination of experiment and computations shows that the apparent pH dependence of hydrogen adsorption in step and defect sites of platinum electrodes is due to the co‐adsorption of cations with hydroxyl. A model for this effect, which is of key importance for interpreting the electrocatalytic activity of platinum, is outlined.
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•AMGO was synthesized through a facile one-step chemical route for adsorption of Cr(VI).•Cr(VI) was reduced to the Cr(III) and thus improved the adsorption capacity.•AMGO can be ...easily separated from aqueous solution by external magnetic field.
A novel ternary magnetic composite consisting of graphene oxide (GO), diethylenetriamine and Fe3O4 nanoparticles (AMGO) were synthesized by a facile one-step reaction route and characterized. The AMGO was applied as a magnetic adsorbent for the Cr(VI) removal from aqueous solutions and the magnetic separation process only took 40s. The maximum adsorption capacity of the AMGO for Cr(VI) was 123.4mg/g, displaying a high efficiency for the removal of Cr(VI), which was much higher than that of MGO. The removal process was pH dependence, endothermic and spontaneous. The pseudo-second-order model described well the adsorption kinetic data and the Langmuir isotherm model fitted the experimental data better than the Freundlich isotherm model. XPS analysis revealed that the Cr(VI) was reduced to the low-toxicity Cr(III) during the adsorption process. Both the Cr(VI) adsorption and subsequent reduction of adsorbed Cr(VI) to Cr(III) contributed to the Cr(VI) removal. In addition, the excellent reproducibility indicate that the AMGO may be a promising adsorption material for the separation and preconcentration of Cr(VI) ions from aqueous solutions in environmental pollution cleanup.
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