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Effects of Pd nanoclusters in PdxSn100-x/Ni electrodes with preferred diffraction planes of Sn(101) and Sn(200) plated on a nickel foam were studied on electrochemical reduction reaction of nitrate (NO3-). NO3- converted to NO2-, N2 and NH4+ by surface Hads was assessed at different Pd to Sn ratio through the electroanalysis and batch electrolysis at constant current mode. Pd loading obviously enhanced the current density of proton diffusion-controlled Sn0/Sn(II) transition. NO3- reduction was much more efficient on PdSn(200) than on PdSn(101); 53% of N2 yield on Sn(200)/Ni could increase up to 79% on Pd5Sn(200)95/Ni, while further increasing Pd loading would gradually increase NH4+ yield. The steady-state kinetics proposed a scheme of adsorption and deoxygenation of NO3- on Sn(200) and hydrogenation of NO2- to N2 on Pd NPs beside the Sn crystals.

An electrode made of activated carbon that had high-specific-surface area and low pHzpc supported on graphite sheet was fabricated. The electrode, NSA/G, was used to study the effect of reversible surface charge on the adsorption of simple electrolyte, i.e., NaCl, on polarizable electrode. Polarizable surface charge is originated from externally applied potential whereas reversible surface charge is derived from change of activity of potential-determining ions, i.e., H+ or OH– owning to hydrous surface, which undergoes protonation and deprotonation of surface hydroxyl groups. Ion adsorption density was obtained from direct analytical measurement of corresponding ion studied instead of conductivity measurement. Langmuir adsorption isotherm was applied to estimate the monolayer ion adsorption density. Electrosorption/desorption kinetics was fitted well by the first-order rate law. In the applied potential range of −0.3 to −1.0 V (vs. SCE) and pH of 3 to 10, the pH-determining surface, i.e., reversible charge, accounted for Na+ sorption intensity was estimated based on the Gouy-Chapman version of electrical double layer theory. Results revealed that the two major surface charges, i.e., polarizable (σE) and reversible (σpH), contributed equally to the total charge density (σT). At high pH (pH 10) and low applied voltage (-0.3 V vs. SCE), the fraction of pH-determining contribution to total surface charge with respect to Na+ sorption, i.e., σpH/σT, was around 0.50. Results reaffirmed the importance of reversible surface charge together with polarizable surface charge on the design and operation of CDI system for electrosorption of ions from water.

In-situ chlorine generation has high disinfection potential for small to medium scale water treatment systems. Electrodes were prepared by coating Pt-, Ni-, Co-oxides on graphite substrate using electrodeless deposition method and characterized with SEM, EDS, XRD, XPS and cyclic voltammetry. Results showed that the molar ratio of Ni- and Co-oxides on graphite surface influenced surface structure and in-situ chlorine generation capacity. Pt0.01Ni0.24Co0.75 electrode exhibited a unique surface structure and the highest in-situ chlorine generation capability. The Pt0.01Ni0.24Co0.75-G electrode exhibited highly porous 3D structure and high oxygen deficit, which significantly promoted the formation of M-Cl− binding on electrode surface and enhanced chlorine generation. The onset of chlorine evolution potential was lower than that of oxygen on Pt0.01Ni0.24Co0.75-G electrode. Moreover, the transfer coefficient of chloride oxidation was smaller than that of water oxidation, which would enhance chloride oxidation current efficiency. The in-situ chlorine generation capability increased with NaCl concentration. The kinetics of chlorine generation was well described by the Langmuir-Hinsheldwood mechanism. The in-situ disinfection rate decreased with the increase in initial E. coli density. A 7.5-log disinfection was achieved in 15 min in the presence of 0.01 M NaCl under 5 mA/cm2 current density at room temperature. The lipid peroxide, morphology changes and destruction of E. coli cell membrane were observed in the in-situ disinfection process, indicating that reactive species such as chlorine radical in addition to free chlorine played the main role of in-situ disinfection.

Mesoporous zirconium pyrophosphate(ZPP) adsorbents were synthesized, with six quaternary ammonium salts (Quats), namely, Octyltrimethylammonium (OTMA, C8), Decyltrimethylammonium (DCTMA, C10), Dodecyltrimethylammonium (DDTMA, C12), Tetradecyltrimethylammonium (TDTMA, C14), Hexadecyltrimethylammoium (HDTMA, C16), and Octadecyltrimethylammonium (ODTMA, C18), as template for studying fluoride adsorption. Quats of long carbon chain length significantly affected the specific surface area of mesoporous ZPP adsorbents. C18-ZPP exhibited the largest specific surface area and fluoride adsorption density. Fluoride adsorption density remained constant at pH 10–11. Langmuir adsorption isotherm described fluoride adsorption characteristics well. Results showed that mesoporous ZPP synthesized with C18 at Zr to C18 molar ratio of 0.57:1 exhibited the best fluoride adsorption capacity (32 mmol/g) among all ZPP adsorbents prepared at various Zr to C18 molar ratios. C18-ZPP exhibited two-fold increase in fluoride removal capacity compared to plain ZPP. The reusability of C18-ZPP was assessed by running fluoride removal at least five cycles. Mesoporous ZPP is a promising adsorbent for fluoride removal from water with much enhanced adsorption capacity, regenerability, and reusability.

The capability of manganese dioxide (MnO2) supported on loofah-derived activated carbon (AC) in the electrosorptive removal of common inert ions was studied in constant potential mode. Four MnO2 polymorphs were prepared by redox chemical precipitation and characterized by XRD, SEM, BET and XPS. The pseudocapacitance property of the MnO2/AC electrode, significantly affected by the surface- and diffusion-controlled charge storage mechanism, was assessed via voltammetry and modified Langmuir adsorption isotherm. Batch electrosorption experiments were then performed at constant potential in the range of −1.5 V to + 1.5 V (vs. Ag/AgCl) using AC and α-MnO2/AC electrodes in the presence of common simple electrolytes, including NaNO3, Li2SO4, and Ca(ClO4)2. Consequently, the applied working potential (Eapp) positively affected the ion electrosorption rate and capacity. Faradaic processes occurred on MnO2, i.e., Mn(III)/Mn(IV) transition, increased the diffusion capacitance of AC, thus enhancing the first-order rate and monolayer capacity, mainly for the electrosorption of cations. Results showed that ion solvation, controlled by the ionic radius and valence of an ion, which impacted ion intercalation in MnO2 and affected ion adsorption characteristics. The cation sorption capacity of α-MnO2/AC followed the order of Na+ (2.8 × 10-4 mol g−1) > Ca2+ (2.1 × 10-4 mol g−1) > Li+ (0.76 × 10-4 mol g−1) at Eapp = -1.5 V. The differential capacitance as affected by polarized potential and the shift of zero net charge or IEP toward more positively charging potential further highlighted the contribution of pseudocapacitance to ion adsorption on α-MnO2/AC electrode.