Electrocatalytic reduction of nitrate to ammonia by Pd/In modified Nickel foam electrode in aqueous solution.

Nitrate pollution in surface water and ground water has drawn wide attention, which has brought challenges to human health and natural ecology. Electroreduction of nitrate to NH3 in waste water was a way to turn waste into wealth, which has attracted interest of many researchers. Using Nickel foam as substrate, we prepared Pd/In bimetallic electrode (NF-Pd/In) according to a two-step electrodeposition method. There are many irregularly shaped particles in the size range of 10 nm-100 nm accumulated on the surface of prepared NF-Pd/In electrode, which could supply high specific area and more active sites for nitrate electroreduction. FESEM-EDS, XRD and XPS analysis confirmed the uniform distribution of Pd and In on the surface of prepared NF-Pd/In electrode, with a mass ratio of 4.5/1. Above 96% of 100 mg/L NO3--N was removed and 95% of NH3 selectivity was reached after 5 h of reaction under -1.6 V vs. Ag/AgCl sat. KCl when using 0.05 mol/L of Na2SO4 as electrolyte. High concentration of NaCl (0.05 mol/L) in the test solution dramatically decreased the NH3 selectivity because the produced NH3 could be further oxidized to N2 by the formed HClO from Cl-. EIS tests indicated that the prepared NF-Pd/In electrode showed much lower electrode resistance than NF due to the adsorptive property and electrocatalytic ability for nitrate removal. Density functional theory (DFT) calculations indicated that the presence of In could promote the conversion of NO3- to *NO3 during the process of nitrate electroreduction to NH3. Circulating tests demonstrated the stability of prepared NF-Pd/In electrode.

Pd/Cu bimetallic nano-catalyst supported on anion exchange resin (A520E) for nitrate removal from water: High property and stability.

High nitrate concentration in water can lead to eutrophication and the disruption of healthy aquatic ecosystems. Additionally, in the human digestive system, it has the potential to be reduced to nitrite, which can be damaging to people's physical health. Catalytic hydrogenation of nitrate is one of the strategies for removing nitrate from water. Using A520E resin as support, we prepared Pd/Cu nano-catalyst (Pd/Cu@A520E) according to a liquid phase reduction method. A520E could improve the transfer process of nitrate in the solution to the activity sites of Pd/Cu nanoparticles, thus increase the reaction rate of nitrate reduction. Pd/Cu bimetallic nano-particles were evenly distributed on/in the resin with a size range from 2 nm to 10 nm. The External Circulating System equipped with Venturi tube (ECSV) was designed to improve the utilization efficiency of H2 in both batch tests and long-term continuous-flow tests. Nearly 100% of nitrate removal efficiency and above 90% of N2 selectivity were achieved in both batch tests and continuous-flow tests. Coexisting Cl- and SO42- at 300 mg/L showed little impact on the property of Pd/Cu@A520E. Pd/Cu@A520E also showed high nitrate removal property and stability in continuous-flow tests of more than 800 h. NO3- was adsorbed onto the active sites (functional groups and Pd/Cu particle sites), meanwhile H2 was adsorbed onto the active sites of Pd/Cu@A520E to form Pd [H]. Then the adsorbed NO3- was reduced into N2 (main product) or NH4+ by Pd [H]. In addition, Pd/Cu@A520E showed high nitrate removal property from municipal waste water.

Practical application of Pd-based bimetallic catalysts with enhanced selectivity supported by chelating resin for catalytic nitrate reduction in real water.

An innovative Pd-Me (Pd-Cu, Pd-In and Pd-Sn) bimetallic catalyst supported on porous chelating DOWEX M4195 resin (D) was established to reduce the nitrate almost entirely and achieved high selectivity to the expected harmless form of nitrogen. In this study, sodium borohydride (NaBH4) was applied in preparing bimetallic catalysts by liquid-phase reduction as the prestoring reductant. Pd-In/D and Pd-Sn/D groups performed well in N2selectivity (all above 97%). In addition, Pd-In and Pd-Sn bimetallic catalysis yields higher selectivity towards N2than the Pd-Cu pair in the presence of HCO3-, Cl-, SO42-and humic acid. Likewise, in terms of N2selectivity, Pd-In/D and Pd-Sn/D bimetallic catalysts were superior to that of Pd-Cu/D (72.16%) in the municipal wastewater treatment plant sewage. The current results provide insight into the superb reactivity, excellent stability, and most important-extremely high harmless N2selectivity of Pd-In and Pd-Sn-based bimetallic catalysts in practical application and provide new ideas for enhancing the feasibility of the catalytic reduction of nitrate by minimizing environmentally harmful by-products.

Preparing Pd/Sn modified nickel foam electrode for nitrate removal from aqueous solutions.

Nitrate pollution in ground water and surface water has been becoming a worldwide problem that poses a great challenge to steady water ecosystem and human health. Electrochemical reduction is a promising way to remove nitrate from water because of advantages. We prepared Pd/Sn modified nickel foam (NF) electrode according to a two-step electrodeposition method. The prepared NF-Pd/Sn electrode showed a micromorphology like "Karst Fengcong" with peaks, saddles and nadirs intertwined with each other. Pd0 and Sn0 were detected on the NF-Pd/Sn electrode and the mass ratio of Pd/Sn was 4.3/1. The NF-Pd/Sn electrode showed the highest reaction rate (kobs: 0.543 h-1) and removal efficiency (94%) under the condition of 100 mg N/L, 0.05 mol/L Na2SO4 and -1.6 V vs. Ag/AgCl sat. KCl. The highest N2-selectivity (100%) was reached under the condition of 100 mg N/L, 0.05 mol/L NaCl and -1.6 V vs. Ag/AgCl sat. KCl. The microstructure of NF-Pd/Sn electrode like "Karst Fengcong" could provide large specific surface area and more active sites for nitrate adsorption and electrocatalytic reduction in aqueous solution. The adsorption and the reduction reaction of nitrate on the surface of NF-Pd/Sn could increase the electric current response in the test system.

Preparing porous Cu/Pd electrode on nickel foam using hydrogen bubbles dynamic template for high-efficiency and high-stability removal of nitrate from water.

Electrochemical reduction is a promising technology to remove nitrate from water. The metallic composition and geometry of electrodes usually dominate the nitrate removal property. Based on nickel foam (NF), we prepared Cu/Pd bimetallic electrode using hydrogen bubbles dynamic template according to a two-step electrodeposition method (Pd after Cu). The micromorphology, crystal structure, and metallic composition were analyzed by using the field emission scanning electron microscope with energy dispersive spectroscopy (FESEM-EDS), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) instruments, respectively. 4.4 mg of Cu and 1.4 mg of Pd were detected on the prepared Cu/Pd electrode. The micromorphology of prepared Cu/Pd electrode showed a grape-bunch look with porous structure of two stage sizes (100-500 nm and 200-300 µm). 98% of the initial NO3--N (100 mg/L) was removed under the potential of - 1.6 V vs. Ag/AgCl saturated KCl after 24 h of reaction when using 0.05 mol/L of Na2SO4 or NaCl as electrolyte. But the concentration of produced NH4+-N was higher than 80 mg/L when using Na2SO4 as electrolyte, which was close to 0 mg/L when using NaCl as electrolyte. The cyclic voltammetry curves of 1000 cycles and the long-term continuous flow test of about 200 h suggested that the prepared Cu/Pd electrode showed high stability for nitrate removal from water.

Performance of Pd/Sn catalysts supported by chelating resin prestoring reductant for nitrate reduction in actual water.

Catalytic hydrogen reduction has appeared as a promising strategy for chemical denitrification with advantages of high activity and simple operation. However, the risk and low utilization of H2 is the disadvantage of catalytic hydrogen reduction. In recent years, catalytic reduction reactions in the presence of sodium borohydride (NaBH4) have been extensively studied. NaBH4 can be used as an electron source to generate electrons on the surface of the catalyst and can catalyze the reduction of pollutants. But it makes commercialization costly and causes significant environmental pollution if widely use NaBH4. In this study, we prepared supported Pd/Sn bimetallic nanoparticles which could adsorb NaBH4 during the preparation of the Pd/Sn bimetallic catalyst as the prestoring reductant. No additional reducing agent is required during nitrate reduction process. The performance and mechanism for nitrate reduction by using Pd/Sn bimetallic nanoparticles were discussed. Moreover, the catalyst D-Pd1/Sn1 reached a complete nitrate removal in the municipal wastewater treatment plant effluent water within 3 h. The results provide a prospect for denitrification in biological wastewater treatment plants.

A new supported Cu/Pd bimetallic nanoparticles composites prestoring reductant for nitrate removal: high reactivity and N2 selectivity.

Catalytic hydrogen reduction appears to be a promising strategy for nitrate removal. However, the danger and low utilization of H2 are the disadvantages of catalytic hydrogen reduction. Sodium borohydride (NaBH4), considered a potential candidate for hydrogen storage, has been investigated as an electron source for the catalytic reduction of contaminants. However, extensive use of NaBH4 makes commercialization costly and causes environmental pollution. In this study, we prepared supported Cu/Pd bimetallic nanoparticles that could prestore hydrogen. No additional reducing agent was required during the nitrate reduction process. The performance and mechanism of Cu/Pd bimetallic nanoparticles for nitrate reduction are discussed. Good performance was obtained with high reactivity (99.04% nitrate removal efficiency) and high selectivity for N2 (94.71%). The Cu/Pd bimetallic catalyst could be recovered by NaBH4 for 5 cycles. Moreover, a 97.49% nitrate removal efficiency was obtained for actual wastewater, indicating good prospects for nitrate reduction applications.

Simultaneous removal of nitrate/phosphate with bimetallic nanoparticles of Fe coupled with copper or nickel supported on chelating resin.

Given the prevalence of nitrate and phosphate in surface and groundwater, it is important to develop technology for the simultaneous removal of nitrate and phosphate. In this study, we prepared the bimetallic nanoparticles of Fe coupled with copper or nickel supported on chelating resin DOW 3N (D-Fe/Ni and D-Fe/Cu) for removing nitrate and phosphate simultaneously. XPS profiles revealed that Cu has better ability than Ni to increase the stability of Fe nanoparticles and prevent nZVI from oxidation. The results showed that nitrate removal efficiencies by D-Fe/Ni and D-Fe/Cu were 98.7% and 95.5%, respectively and the phosphate removal efficiencies of D-Fe/Cu and D-Fe/Ni were 99.0% and 93.0%, respectively. Besides adsorption and coprecipitation as reported in previous studies, the mechanism of phosphate removal also includes the adsorption of the newly formed polymeric ligand exchanger (PLE). Moreover, in previous studies, the presence of phosphate had significant negative effects on the reduction of nitrate. However, in this study, the removal efficiency of nitrate was less affected with the increasing concentration of phosphate for D-Fe/Cu. This was mainly because D-Fe/Cu had higher adsorption capacity of phosphate due to the newly formed PLE according to the XPS depth profile analysis.

Synergy of lignocelluloses pretreatment by sodium carbonate and bacterium to enhance enzymatic hydrolysis of rice straw.

We studied a new strategy for pretreatment of rice straw (RS) to enhance enzymatic hydrolysis under mild condition. This approach uses the synergy of sodium carbonate (Na2CO3) and the bacterial strain Cupriavidus basilensis B-8 (hereafter B-8). After synergistic Na2CO3 and B-8 pretreatment (SNBP), the reducing sugar yield varied from 335.3mg/g to 799.6mg/g under different conditions. This increased by 13-31% over Na2CO3 pretreatment (284.2-719.2mg/g) and 3.42-8.15times over the untreated RS (98mg/g). Moreover, the composition of RS was changed significantly through decreases in lignin and hemicellulose. We confirmed this change by compositional analysis and physicochemical characterization of the structure of RS before and after pretreatment. We also elaborated a mechanism for SNBP to better explain RS changes and bacterial effects on enzymatic hydrolysis.

Effect of optimized three-component antiscalant mixture on calcium carbonate scale deposition.

The mixture of 1-hydroxyethane-1,1-diphosphonic acid (HEDP), and polyacrylic acid (PAA) and synthesized hydrolyzed polymaleic anhydride (HPMA) was optimized by using simplex lattice of Design-Expert software through calcium carbonate precipitation method. The optimum mass ratio of HEDP, PAA and synthesized HPMA was obtained at 10/10/80, which showed excellent performance on controlling calcium carbonate deposition. The antiscale efficiency of the optimum mixture was 84% and 95%, respectively, in the calcium carbonate precipitation test and the calcium carbonate scale deposit test. The optimum mixture could disturb the crystal growth of calcium carbonate and then affect the morphology and crystal structure of the calcium carbonate precipitates.

Inhibition effect of phosphorus-based chemicals on corrosion of carbon steel in secondary-treated municipal wastewater.

Secondary-treated municipal wastewater (MWW) could supply a viable alternative water resource for cooling water systems. Inorganic salts in the concentrated cooling water pose a great challenge to corrosion control chemicals. In this study, the inhibition effect of 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP), trimethylene phosphonic acid (ATMP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) on corrosion of carbon steel in secondary-treated MWW was investigated by the means of potentiodynamic polarization and electrochemical impedance spectroscopy. The inhibition effect increased with increasing concentration of inhibitors. The corrosion rates of carbon steel were 1.5, 0.8, 0.2 and 0.5 mm a(-1) for blank, HEDP, ATMP and PBTCA samples at 50 mg L(-1), respectively. The phosphorus-based chemicals could adsorb onto the surface of the carbon steel electrode, form a coat of protective film and then protect the carbon steel from corrosion in the test solution.