Preparation of Fe/C-MgCO3 micro-electrolysis fillers and mechanism of phosphorus removal.

Iron-carbon micro-electrolysis is effective for the removal of phosphorus in wastewater; however, meeting the stringent emission standards required for treatment is difficult. To meet these treatment standards, modified micro-electrolytic fillers were prepared from iron dust, powdered activated carbon, clay, and additives using an elevated temperature roasting process under an inert atmosphere. The results show that among several additives, the modified micro-electrolytic (Fe/C-MgCO3) fillers using MgCO3 were the most effective at phosphorus removal. The preparation conditions for the Fe/C-MgCO3 fillers and their effects on phosphorus removal performance were investigated. Under the optimal preparation conditions (calcination temperature: 800 °C, Fe/C = 4:1, clay content 20%, and 5% MgCO3), the filler yielded a high compressive strength of 3.5 MPa, 1 h water absorption rate of 25.7%, and specific surface area and apparent density of 154.2 m2/g and 2689.2 kg/m3, respectively. The iron-carbon micro-electrolysis process removed 97% of phosphorus in the wastewater by using the Fe/C-MgCO3 fillers, which was 14% more than the Fe/C filler. Electrostatic adsorption and surface precipitation were identified as the main phosphorus removal mechanisms, and the surface of the Fe/C-MgCO3 filler was continuously updated. These results demonstrated that Fe/C-MgCO3 is a promising filler for phosphorus removal in water treatment.

Electrochemical study of a novel high-efficiency PbO2 anode based on a cerium-graphene oxide co-doping strategy: Electrodeposition mechanism, parameter optimization, and degradation pathways.

A novel and efficient Ti/SnO2-Sb/PbO2-GO-Ce electrode was successfully fabricated based on the co-deposition of Ce ions and graphene oxide (GO) into ß-PbO2 crystals and used as an anode for electrocatalytic oxidation of phenol. The electrodeposition mechanism, parameter optimization, mechanism analysis, and potential degradation pathways were discussed in depth. The co-doping of GO and Ce resulted in the high directional specificity of ß(301), orderly and dense grain arrangement of PbO2 crystals. At the same time, the oxygen evolution potential, •OH generation capacity and lifetime were also improved. The effects of experimental parameters on phenol removal efficiency were evaluated, including the applied current density, electrode gap, supporting electrolyte, initial NaCl concentration, initial pH, and initial phenol concentration. Under the optimal conditions, the removal efficiency of phenol can reach 375.6 g m-2 h-1 for 20 min electrolysis, which is about 1.2 times that of the pure PbO2 electrode. The active oxygen species (•OH, ClO- and HClO) were important attributes to the degradation of phenol. Additionally, a potential degradation pathway for phenol was proposed. After 10 successive recycles, there was no significant difference of the electro-generated •OH, cell voltage and phenol removal rate, which confirms the stability and admirable reusability of Ti/SnO2-Sb/PbO2-GO-Ce electrode.

Pilot-scale microsand-ballasted flocculation of wastewater: turbidity removal, parameters optimization, and mechanism analysis.

The flocs formed during microsand-ballasted flocculation (MBF) have attracted much attention. However, few studies have reported on comprehensive process parameters of MBF and its mechanism is still not well understood. Jar test and pilot-scale continuous experiments were here conducted on two kinds of simulated wastewater, labeled S1 (21.6-25.9 NTU) and S2 (96-105 NTU). Results revealed the hydraulic retention time ratio in the coagulation cell, injection and maturation cell, lamella settler of pilot-scale MBF equipment was 1:3:7.3. The optimum poly aluminum chloride doses for samples S1 and S2 were 0.875 g/L and 1.0 g/L. Besides, the optimum size of microsand was 49-106 µm and the optimum dose was 1.0 g/L. Under aforementioned conditions, the effluent turbidity of S1 was below 0.47 NTU, even lower than the Chinese drinking water standard; that of S2 was below 1.7 NTU, meeting the Chinese recycled water standard. Turbidity removal ranged from 98.0 to 98.8% for S1 and 98.5 to 99.5% for S2 when microsand was added. Therefore, microsand addition enhances MBF performance, where microsand serves as an initial core particle. Some microsand core particles bond together to form a dense core structure of micro-flocs by the adsorption bridging of inorganic polymeric flocculant. Moreover, the size of the largest micro-flocs may be controllable as long as the effective energy dissipation coefficient is adjusted appropriately through specific stirring speeds. This work provides comprehensive pilot-scale process parameters for using MBF to effectively treat wastewater and offers a clearer explanation of the formation mechanism of microsand-ballasted flocs.

Photoelectrochemical characterization of a robust TiO2/BDD heterojunction electrode for sensing application in aqueous solutions.

Titanium dioxide (TiO(2)) and boron-doped diamond (BDD) are two of the most popular functional materials in recent years. In this work, TiO(2) nanoparticles were immobilized onto the BDD electrodes by a dip-coating technique. Continuous and uniform mixed-phase (anatase and rutile) and pure-anatase TiO(2)/BDD electrodes were obtained after calcination processes at 700 and 450 degrees C, respectively. The particle sizes of both types of TiO(2) film range from 20 to 30 nm. In comparison with a TiO(2)/indium tin oxide (ITO) electrode, the TiO(2)/BDD electrode demonstrates a higher photoelectrocatalytic activity toward the oxidation of organic compounds, such as glucose and potassium hydrogen phthalate. Among all the tested TiO(2) electrodes, the mixed-phase TiO(2)/BDD electrode demonstrated the highest photoelectrocatalytic activity, which can be attributed to the formation of the p-n heterojunction between TiO(2) and BDD. The electrode was subsequently used to detect a wide spectrum of organic compounds in aqueous solution using a steady-state current method. An excellent linear relationship between the steady-state photocurrents and equivalent organic concentrations was attained. The steady-state oxidation photocurrents of the mixed-phase TiO(2)/BDD electrode were insensitive to pH in the range of pH 2-10. Furthermore, the electrodes exhibited excellent robustness under strong acidic conditions that the TiO(2)/ITO electrodes cannot stand. These characteristics bestow the mixed-phase TiO(2)/BDD electrode to be a versatile material for the sensing of organic compounds.

Degradation of nitrobenzene by synchronistic oxidation and reduction in an internal circulation microelectrolysis reactor.

The degradation of nitrobenzene by synchronistic oxidation and reduction was investigated using an internal circulation microelectrolysis (ICE) reactor with an active volume of 0.018 m3. Compared with a conventional fixed bed reactor with and without aeration, the ICE reactor exhibited a markedly higher nitrobenzene degradation efficiency. The effects of various operational parameters such as reaction time, aeration rate, initial nitrobenzene concentration, initial pH, and a volume ratio of iron and carbon (Fe/C) were also investigated. The optimal operating conditions (reaction time = 60 min, aeration rate = 5 × 10-4 m3/s, initial concentration of nitrobenzene = 300 mg/L, pH = 3.0, Fe/C = 1:1) gave removal efficiencies of nitrobenzene and chemical oxygen demand of 98.2% and 58%, respectively. The biodegradability index of the treated nitrobenzene solution was 0.45, which is 22 times that of the original solution. The reaction intermediates were identified through high-performance liquid chromatography, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, gas chromatography-mass spectrometry, and ion chromatography. The primary intermediates were determined to be aniline, phenol, and carboxylic acids, indicating that nitrobenzene was synchronously oxidized and reduced in the ICE reactor. Based on the identified intermediates, a possible pathway for nitrobenzene degradation in the ICE reactor is proposed.

Photoelectrocatalytic activity of an ordered and vertically aligned TiO2 nanorod array/BDD heterojunction electrode.

Rutile TiO2 nanorod (TiNR) arrays were fabricated on a boron-doped diamond (BDD) substrate by a simple hydrothermal synthesis method. A fluorine-doped tin oxide (FTO) electrode grown with TiNR arrays was also prepared using the same technology for comparison. Field-emission scanning electron microscopy results show that oriented TiNR arrays can grow vertically on the surface of BDD and FTO electrodes. TiNR arrays grown on both electrodes had the same length (3µm). In comparison with the TiNR/FTO electrode, the TiNR/BDD electrode demonstrated a higher photoelectrocatalytic activity for the degradation of water and organic compounds, which is mostly attributed to the formation of a p-n heterojunction between the TiNR arrays and BDD at high potential, apart from the density of TiNR. A linear relationship between the photoelectrocatalytic current and the organic concentration can be observed on both electrodes. However, the linear range between net photoelectrocatalytic current values and organic compound concentrations for the TiNR/BDD electrode are much greater than those for the TiNR/FTO electrode, which makes the TiNR/BDD electrode a versatile material for the photocatalytic degradation and sensing of organic compounds.

Electrochemically enhanced adsorption of phenol on activated carbon fibers in basic aqueous solution.

Electrosorption isotherms and thermodynamics of phenol on activated carbon fibers (ACFs) in basic solution, as well as the factors (bias potential, initial concentration, and electrolyte) affecting adsorption/electrosorption kinetics, were investigated. The kinetics, which followed the Lagergren adsorption rate law, exhibited a variety of responses depending on bias potential, initial concentration, and electrolyte. The electrosorption isotherms were in agreement with the classical models of Langmuir and Freundlich, but the former gave more satisfactory correlation coefficients. With electrosorption at a bias potential of 700 mV from the basic solution, a nearly 10-fold enhancement of maximum adsorption capacity was achievable. The electrosorption free energy (DeltaG(ads)), enthalpy (DeltaH(ads)), and entropy (DeltaS(ads)) of phenol on the ACFs were calculated from adsorption isotherms at different temperatures. The results indicated that electrosorption of phenol in basic solution was spontaneous and exothermic. Furthermore, it was assessed that electrosorption occurred by dipole-dipole interaction with DeltaH(ads) of -20.14 kJ mol(-1) besides suppositional electrostatic interaction.

A selective etching phenomenon on {001} faceted anatase titanium dioxide single crystal surfaces by hydrofluoric acid.

A selective etching phenomenon on {001} faceted anatase TiO(2) single crystal surfaces by HF and associated etching mechanism are reported. Density functional theory (DFT) calculations reveal that HF stabilizes the grown {001} facets at low concentrations, but selectively destroys the grown {001} facets at high concentrations.

Anatase TiO2 crystal facet growth: mechanistic role of hydrofluoric acid and photoelectrocatalytic activity.

This work reports a facile hydrothermal approach to directly grow anatase TiO(2) crystals with exposed {001} facets on titanium foil substrate by controlling pH of HF solution. The mechanistic role of HF for control growth of the crystal facet of anatase TiO(2) crystals has been investigated. The results demonstrate that controlling solution pH controls the extent of surface fluorination of anatase TiO(2), hence the size, shape, morphology, and {001} faceted surface area of TiO(2) crystals. The theoretical calculations reveal that {001} faceted surface fluorination of anatase TiO(2) can merely occur via dissociative adsorption of HF molecules under acidic conditions while the adsorption of Na(+)F(-) is thermodynamically prohibited. This confirms that the presence of molecular form of HF but not F(-) is essential for preservation of exposed {001} facets of anatase TiO(2). Anatase TiO(2) crystals with exposed {001} facets can be directly fabricated on titanium foil by controlling the solution pH ≤ 5.8. When pH is increased to near neutral and beyond (e.g., pH ≥ 6.6), the insufficient concentration of HF ([HF] ≤ 0.04%) dramatically reduces the extent of surface fluorination, leading to the formation of anatase TiO(2) crystals with {101} facets and titanate nanorods/nanosheets. The anatase TiO(2) nanocrystals with exposed {001} facets exhibits a superior photoelectrocatalytic activity toward water oxidation. The findings of this work clarify the mechanistic role of HF for controlling the crystal facet growth, providing a facile means for massive production of desired nanostructures with high reactive facets on solid substrates for other metal oxides.

Anatase TiO(2) microspheres with exposed mirror-like plane {001} facets for high performance dye-sensitized solar cells (DSSCs).

Anatase TiO(2) microspheres with exposed mirror-like plane {001} facets were successfully synthesized via a facile hydrothermal process. The photoanode composed of TiO(2) microsphere top layer shows an improved DSSCs efficiency owing to the superior light scattering effect of microspheres and excellent light reflecting ability of the mirror-like plane {001} facets.

[Kinetics of enhanced adsorption by polarization for organic pollutants on activated carbon fiber].

The adsorption kinetics for model pollutants on the activated carbon fiber (ACF) by polarization was investigated. Kinetics data obtained for the adsorption of these model pollutants at open-circuit and 400mV, -400mV polarization was applied to the Lagergren equation, and adsorption rate constants (Ka) were determined. With the anodic polarization of 400mV, the capacity of sodium phenoxide increases from 0.0083mmol x g(-1) at open-circuit to 0.18mmol x g(-1), and a seventeen-fold enhancement is achievable; however, the capacity of p-nitrophenol decreases from 2.93 mmol x g(-1) at open-circuit to 2.65 mmol x g(-1). With the cathodal polarization of -400mV, the capacity of aniline improves from 3.60 mmol x g(-1) at open-circuit to 3.88 mmol x g(-1); however, the capacity of sodium dodecylbenzene sulfonate reduces from 2.20 mmol x g(-1) at open-circuit to 1.59 mmol x g(-1). The enhancement for electrosorption changes with different groups substituting. Anodic polarization enhances the adsorption of benzene with electron-donating group. But whether anodic or not cathodal polarization has less effect on the adsorption of electron-accepting aromatic compounds, and decreases the adsorption of benzene bearing donor-conjugate bridge-acceptor but increases the adsorption rate. Electrostatic interaction plays a very important role in electrosorption of ion-pollutants.