Characterization of the removal of Chromium(VI) from groundwater by electrocoagulation

A batch electrocoagulation system has been evaluated for the removal of Cr(VI) from brackish groundwater under different operating conditions. The influence of electrode type, applied current density, initial pH, initial chromium concentration, conductivity and temperature were evaluated. The experimental results indicated that chromium removal increased with increasing the applied current density and conductivity. The efficiency of different electrode arrangements (iron, aluminum) was also assessed, and indicated that Fe–Fe electrode pair was the most efficient arrangement and was able to achieve 100% Cr removal at an electrocoagulation time of 5 min, a current density of 7.94 mA/cm², and pH of 8 at room temperature 25 °C. The generated sludge for the iron electrodes was characterized using EDS, X-ray fluorescence (XRF) and FE-SEM. The analysis confirmed the formation and precipitation of Fe(OH)₃ and Cr(OH)₃ as solids. Overall, the study affirmed that electrocoagulation is a reliable technique for the purification of groundwater with an estimated energy consumption of 0.6 kWh/m³.     

Removal of arsenic from drinking water by the electrocoagulation using Fe and Al electrodes

A novel technique of electrocoagulation (EC) was attempted in the present investigation to remove arsenic from drinking waters. Experiments were carried out in a batch electrochemical reactor using Al and Fe electrodes with monopolar parallel electrode connection mode to assess their efficiency. The effects of several operating parameters on arsenic removal such as pH (4–9), current density (2.5–7.5 A m⁻²), initial concentration (75–500 μg L⁻¹) and operating time (0–15 min) were examined. Optimum operating conditions were determined as an operating time of 12.5 min and pH 6.5 for Fe electrode (93.5%) and 15 min and pH 7 for Al electrode (95.7%) at 2.5 A m⁻², respectively. Arsenic removal obtained was highest with Al electrodes. Operating costs at the optimum conditions were calculated as 0.020 € m⁻³ for Fe and 0.017 € m⁻³ for Al electrodes. EC was able to bring down aqueous phase arsenic concentration to less than 10 μg L⁻¹ with Fe and Al electrodes. The adsorption of arsenic over electrochemically produced hydroxides and metal oxide complexes was found to follow pseudo second-order adsorption model. Scanning electron microscopy was also used to analyze surface topography of the solid particles at Fe/Al electrodes during the EC process.     

Preparation of a composite coagulant: Polymeric aluminum ferric sulfate (PAFS) for wastewater treatment

A new composite coagulant polymeric aluminum ferric was synthesized and parameters affecting the coagulant performance such as reaction temperature and time, and OH/Fe, P/Fe and Al/Fe molar ratios in this study, were examined. In addition, to obtain the optimum synthetic conditions resulting in the maximum turbidity removal efficiency, response surface methodology (RSM) was used to assess their interactive effects on coagulation–flocculation performance. The results showed that reaction temperature (60–80 °C) and time (30–50 min), and OH/Fe (0.1–0.3), P/Fe (0.2–0.3) and Al/Fe (1:9–1:10) molar ratios were favorable to the preparation process. The optimum synthesis conditions were reaction temperature and time, and OH/Fe, P/Fe and Al/Fe molar ratios of 80 °C, 40 min, 0.1, 0.25 and 1:10, respectively. Evaluation of the coagulation–flocculation process showed that COD (chemical oxygen demand) and turbidity removal efficiency of 82.8% and 98.2%, respectively, were achieved at coagulant dosage of 45 mg/L, wastewater initial pH of 8.5, and rapid agitation speed of 250 rpm. In addition, charge neutralization and adsorption/bridging coagulation–flocculation mechanisms played an important role in reducing the surface charge of colloids.     

Activated carbon modified by coupling agent for supercapacitor

A novel and simple strategy by introducing a silane coupling agent into the electrode to improve the supercapacitor performance has been developed in this study. The surface modification of the activated carbon material and the Al current collector are conducted under two different neutral and acidic conditions. The improved electrodes are characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), mechanical tests and electrochemical measurements. The obtained results reveal that the treated activated carbon electrode retains good mechanical properties with decreased bonder content. The electrode prepared using activated carbon treated with the silane coupling agent in acetic acid conditions (pH = 5.0) and a bonder mass content of 7.0% shows the best electrochemical performance. The specific capacitance reaches 352.5 F g^?1, whereas the internal resistance and charge–discharge efficiency are 0.82 Ω and 98.2% respectively.     

Preparation of mullite ceramic microfilter membranes using Response surface methodology based on central composite design

In this paper effect of free silica removal from mullite microfilter membranes using different sodium hydroxide (NaOH) concentrations at different temperatures and for different removal times was studied. The prepared membranes were subjected to XRD, SEM, porosity analysis, and mechanical strength measurement. Response surface methodology (RSM) based on central composite design (CCD) was used to design the experiments and analyze three operating parameters including; NaOH solution concentration, NaOH solution temperature and removal time. The optimum porosity of 49.4 was obtained with NaOH solution concentration of 35 wt% at temperature 75 °C and removal time equal to 8 h.Water flux and mechanical strength as important characteristics were measured for all the membranes. For the membrane with the optimum porosity, water flux, mechanical strength, and free silica removal percentage were 61.7 kg/m² h, 21.6 MPa, and 28.2%, respectively. The maximum rejection percentage was 97.2% and emulsion flux for this state was 15.6 kg/m² h at temperature 25 °C and cross flow velocity of 1.5 m/s.     

Effects of Fe addition on the structure and catalytic performance of mesoporous Mn/Al–SBA-15 catalysts for the reduction of NO with ammonia

Mesoporous Al–SBA-15 has been synthesized by a hydrothermal method and used as a support for Mn/Al–SBA-15, Fe/Al–SBA-15, and Mn–Fe/Al–SBA-15 catalysts. XRD, N₂ sorption, XPS, H₂-TPR and activity tests have been used to assess the properties of catalysts. The Mn–Fe/Al–SBA-15 catalyst exhibited a higher SCR activity than Mn/Al–SBA-15 or Fe/Al–SBA-15 due to a synergistic effect between Mn and Fe. After the addition of Fe, the binding energy of Mn 2p_3/2 on Mn–Fe/Al–SBA-15(573) decreased by about 0.4 eV and the Mn^4 +/Mn^3 + ratio decreased to 1.10. The appropriate Mn^4 +/Mn^3 + ratio may have a great effect on the reduction of NO over Mn–Fe/Al–SBA-15(573) catalyst.     

Modeling and optimizing of electrochemical oxidation of C.I. Reactive Orange 7 on the Ti/Sb–SnO2 as anode via response surface methodology

The decolorization and degradation of an organic dye, Reactive Orange 7 (RO7) in aqueous media by electrochemical oxidation process using Ti/Sb–SnO₂ electrode as anode was modeled and optimized using response surface methodology (RSM) based on central composite design (CCD). The anode electrode was prepared using dip-coating and thermal decomposition method. Accordingly reduced quadratic model was developed to give the substrate color removal efficiency percentage as function of effective parameters such as: initial dye concentration, pH of the solution, electrolyte concentration and current density. The fit of the model is checked by the determination coefficient (R²). In this case, the value of the determination coefficient (R² = 0.9949) is indicated. Maximum color removal efficiency was achieved at the obtained conditions of: pH = 4, concentration of electrolyte = 3.5 g/L and current density = 19 mA/cm². Dye removal rate increased by increasing the concentration of electrolyte, lowering pH and increasing the current density. In optimum conditions, decolorization was obtained completely after 5 min; and the removal of chemical oxygen demand (COD) was reduced to 70.3% after 90 min.     

Fabrication of porous carbon monoliths with a graphitic framework

Macro/mesoporous carbon monoliths with a graphitic framework were synthesized by carbonizing polymeric monoliths of poly(benzoxazine-co-resol). The overall synthesis process consists of the following steps: (a) the preparation of polymeric monoliths by co-polymerization of resorcinol and formaldehyde with a polyamine (tetraethylenepentamine), (b) doping the polymer with a metallic salt of Fe, Ni or Co, (c) carbonization and (d) the removal of inorganic nanoparticles. The metal nanoparticles (Fe, Ni or Co) formed during the carbonization step catalyse the conversion of a fraction of amorphous carbon into graphitic domains. The resulting carbon monoliths contain >50 wt.% of graphitic carbon, which considerably improves their electrical conductivity. The use of tetraethylenepentamine in the synthesis results in a nitrogen-containing framework. Textural characterization of these materials shows that they have a dual porosity made up of macropores and mesopores (∼2–10 nm), with a BET surface area in the 280–400 m² g⁻¹ range. We tested these materials as electrodes in organic electrolyte supercapacitors and found that no conductive additive is needed due to their high electrical conductivity. In addition, they show a specific capacitance of up to 35 F g⁻¹, excellent rate and cycling performance, delivering up to 10 kW kg⁻¹ at high current densities.     

Treatment of textile dyeing wastewater by electrocoagulation using Fe and Al electrodes: optimisation of operating parameters using central composite design

Textile dyeing wastewater was treated by electrocoagulation using aluminium and iron plate electrodes. Response surface methodology and central composite design were applied in the experiments and in statistical data analysis. A current density of 30–100 A m^?2, an initial pH of 4–8, and an operating time of 10–40 min were chosen as independent variables, and the chemical oxygen demand, total organic carbon, and turbidity removal efficiencies and the operating cost were selected as responses in the electrocoagulation process. The developed quadratic models for the responses and the experimental data were in good agreement with model predictions statistically (R² ≥ 0.92, Adj R² ≥ 0.82, and Prob > F < 0.004). The optimised operating variables (initial pH, current density, and operating time) and the maximum total organic carbon, chemical oxygen demand, and turbidity removal efficiencies for textile dyeing wastewater were 5.5, 63.2 A m^?2, 30.4 min, 77%, 82%, and 94% for the iron electrode and 5.6, 52.5 A m^?2, 33.9 min, 68%, 69% and 99% for the aluminium electrode respectively. Minimum operating costs for the iron and aluminium electrodes under optimum conditions were €2.1 m^?3 (€1.0 kg^?1 COD) and €2.4 m^?3 (€1.6 kg^?1 COD). The iron electrode was found to be superior to the aluminium electrode in terms of removal efficiencies and operating cost for the treatment of textile dyeing wastewater.     

Application of nano-sized cobalt on ZSM-5 zeolite as an active catalyst in Fischer–Tropsch synthesis

In this study the catalytic behavior of Co/HZSM-5 in Fischer–Tropsch synthesis (FTS) has been examined in order to optimize the operating conditions for acquiring maximum selectivity. Catalysts consisted of various quantities of cobalt particles supported on HZSM-5 zeolite were prepared by impregnation method. In order to investigate the effects of operating parameters on catalytic performance and to estimate the optimum conditions, experiments were designed using L-16 Taguchi method. All experimental runs were carried out in a fixed bed reactor under isobaric condition (2 MPa). According to the Taguchi model and considering the impact of the operating parameters on the process output and performing certain validation tests, the optimum operating conditions for the process were determined as T = 513 K, space velocity = 1.1 h^?1, Co on HZSM-5 = 11.6%, H₂/CO = 1.7.In the next step, a kinetic model for FTS based on carbide mechanism was presented applying the synthesized catalyst under the optimum conditions. This model is a combination of kinetic rates of hydrocarbon formation and the relations for the growth probability and olefin re-adsorption factor.     

Zinc(II) modified carbon paste electrodes based on self-assembled mercapto compounds-gold-nanoparticles for its determination in water samples

In the present study newly developed potentiometric sensors for determination of zinc(II) are presented. The proposed potentiometric method was based on the fabrication of modified carbon paste (MCPE; electrode X) and modified gold nanoparticles-carbon paste (GNPs-CPE; electrode IX) sensors. A mercapto compound of 1,4-bis(5-mercaptopentyloxy)-benzene (BMPB) alone or self-assembled on gold nanoparticles was used as modifier to construct electrode (X) and electrode (IX) sensors, respectively. The prepared electrodes exhibit Nernstian slope of 29.93 ± 0.4 and 26.0 ± 1.02 mV decade⁻¹ towards Zn(II) ion over a wide concentration range of 6.8 × 10⁻¹⁰ to 2.9 × 10⁻² and 1.0 × 10⁻⁷ to 1.0 × 10⁻² mol L⁻¹ for electrode (IX) and electrode (X) sensors, respectively. The limit of detection of the electrode (IX) and electrode (X) sensors was found to be 6.8 × 10⁻¹⁰ and 1.0 × 10⁻⁷ mol L⁻¹, respectively. The potentiometric response of the electrode (IX) and electrode (X) based on GNPs-BMPB and BMPB are independent of pH of test solution in the pH range of 2.5–8.1 and 3–7 with a response time of 6 and 8 s for electrode (IX) and electrode (X) sensors, respectively. The proposed sensors showed fairly good discriminating ability towards Zn(II) ion in comparison with many hard and soft metal ions. Finally, the proposed electrodes were successfully used as indicator electrodes in potentiometric titration of zinc ion with sodium tetraphenylborate (NaTPB) and in direct determination of Zn(II) ion in some water samples. The results obtained compared well with those obtained using atomic absorption spectrometry.     

Decolourization of the reconstituted dye bath effluent by commercial laccase treatment: Optimization through response surface methodology

This paper aims to study the effect of temperature, pH and enzyme concentration on decolourization of separately two reactive textile dyes (Black Novacron R and Blue Bezaktiv S-GLD 150) used in reconstituted dye bath effluent (textile dye and auxiliary components) and in aqueous dye solutions (dye dissolved in deionised water) by a commercial laccase formulation (DeniLite^® IIS). The central composite design (CCD) matrix and response surface methodology (RSM) have been applied to design experiments for the evaluation of the interactive effects of the three most important operating variables: temperature ‘T’ (25–45 °C), pH (3.0–7.0), and enzyme concentration ‘EC’ (80–240 U/L) on the enzymatic decolourization of the different synthetic dyes solutions at initial dye concentration of 40 mg/L. The RSM indicated that the optimum parameter values were respectively for the reconstituted Black Novacron R and the Blue Bezaktiv S-GLD 150 effluents: T = 43 °C and 41.44 °C, pH 6 and 6.29, EC = 222 and 226.43 U/L. The maximum colour removal was about 98.9% at 593 nm and 79.9% at 400 nm for reconstituted Black Novacron R effluent and about 98.9% at 620 nm for reconstituted Blue Bezaktiv S-GLD 150 effluent. For aqueous dye solutions, RSM has shown that colour removal obtained were quite similar. However, the optimum parameters were different. Hence, enzyme concentration depends on the effluent component.     

Electrochromic properties of Al doped B-subsituted NiO films prepared by sol–gel

In this paper, Al doped B-substituted NiO films were prepared by sol–gel method. The effect of the Al content on the structure of the Al_xB_0.15NiO films were studied with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical and EC properties were examined by cyclic voltammetric (CV) measurements and UV–Vis spectrophotometry, respectively. Al doping could prevent the crystallization of the films, which exhibited much better electrochemical and electrochromic properties than undoped samples. The bleached state absorbance could be significantly lowered when the Al added. EC efficiencies measured at λ = 500 nm of the films with different Al doping content reach ～30 cm² C^?1, with a change in transmittance up to 70%.     

Electrochemical properties of nanodiamond powder electrodes

Detonation-synthesized nanocrystalline diamond is a novel carbon material. Its increased electrical conductivity, due to the features of giant specific surface area and large numbers of surface defects as well as the cluster structure, makes it possible to be used as an electrode material. Nanodiamond powder electrodes were fabricated and the electrochemistry was investigated by cyclic voltammetry and AC impedance measurement. The results show that nanodiamond powder electrode is electrochemically stable in KCl electrolytes over a wide potential range (− 1.2–2.0 V). The electrode reaction is quasi-reversible in 0.1 M KCl containing the ferricyanide–ferrocyanide redox couple. The electrode reaction rate constant k is estimated to be 2.87 × 10^− 3 cm/s. The peak current increases linearly with the rising of the concentration of [Fe(CN)₆]^3−/4−. The AC impedance spectra have been analyzed and an equivalent circuit proposed.     

A kinetic study on hydrochloric acid leaching of nickel from Ni–Al2O3 spent catalyst

Hydrochloric acid leaching of nickel from spent Ni–Al₂O₃ catalyst (12.7% Ni, 39.2% Al and 0.68% Fe) has been investigated at a range of conditions by varying particle size (50–180 μm), acid concentration (0.025–2 M), pulp density (0.2–0.4%, w/v) and temperature (293–353 K). Nickel was selectively leached from the catalyst, irrespective of the different conditions. Under the most suitable conditions (1 M HCl, 323 K, stirring at 500 rpm, 50–71 μm particle size), the extent of leaching of Ni and Al after 2 h was 99.9% and 1%, respectively. The XRD pattern of the spent catalyst corresponded to crystalline α-Al₂O₃ along with elemental Ni. The peak due to elemental Ni was absent in the residue sample produced at the optimum leaching conditions, confirming the complete dissolution of Ni from the spent catalyst. The leaching results were well fitted with the shrinking core model with apparent activation energy of 17 kJ/mol in the temperature range of 293–353 K indicating a diffusion controlled reaction.     

Comparison of the influence of nanomaterials on response properties of copper selective electrodes

Novel Cu²⁺ ion selective electrode in carbon paste matrices based on incorporation of bis(2-hydroxynaphthaldehydene)-1,6-hexanediamine (BHNHDA) has been developed. The influence of variables including sodium tetraphenylborate (NaTPB), ionophore, and amount of multiwalled carbon nanotubes (MWCNT) and Nujol and effect of two new nanoparticles including gold nanoparticles loaded on activated carbon (Au-NP-AC) and zinc sulfide nanoparticles loaded on activated carbon (ZnS-NP-AC) on the electrodes response was studied and optimized. At optimum specified conditions, the proposed electrodes have appropriate advantages such as short response times and suitable reproducibility and applicability for a period of at least 1 month without any significant divergence in slope and response properties. The sensor based on impregnations of MWCNT, Au-NP-AC and ZnS-NP-AC have wide linear range of concentration (6 × 10^?8–1.0 × 10^?1 mol L^?1) and detection limit of lower than 4 × 10^?8 mol L^?1 of Cu²⁺ ion. The electrodes based on incorporation of Au-NP-AC and ZnS-NP-AC have Nernstian response with slope of 29.34 ± 1.41 and 29.78 ± 1.23 mV decade^?1 and response is independent of pH in the range of 2.0–5.0. Finally, these electrodes have been successfully applied for the determination of Cu²⁺ ions content in various real samples. Due to their acceptable selectivity coefficient, they are usable for accurate and successful evaluation of Cu²⁺ ions content in various real sample with complicated matrices.     

Highly porous carbon spheres for electrochemical capacitors and capacitive flowable suspension electrodes

In flowable and conventional electrochemical capacitors, the energy capacity is largely determined by the electrode material. Spherical active material, with high specific surface area (SSA) represents a promising material candidate for film and flow capacitors. In this study, we synthesized highly porous carbon spheres (CSs) of submicrometer size to investigate their performance in film and suspension electrodes. In particular, we studied the effects of carbonization and activation temperatures on the electrochemical performance of the CSs. The CSs activated at optimum conditions demonstrated narrow pore size distribution (<3 nm) with high SSA (2900 m²/g) and high pore volume (1.3 cc/g), which represent significant improvement as compared to similar materials reported in literature. Electrochemical tests of CSs in 1 M H₂SO₄ solution showed a specific capacitance of 154 F/g for suspension electrode and 168 F/g for film electrode with excellent rate performance (capacitive behaviors up to 100 mV/s) and cycling performance (95% of initial capacitance after 5000 cycles). Moreover, in the film electrode configuration, CSs exhibited high rate performance (78 F/g at 1000 mV/s) and volumetric power density (9000 W/L) in organic electrolytes, along with high energy density (21.4 Wh/L) in ionic liquids.     

Mesoporous carbons synthesized by direct carbonization of citrate salts for use as high-performance capacitors

A simple one-step synthesis methodology for the fabrication of mesoporous carbons with an excellent performance as supercapacitor electrodes is presented. The procedure is based on the carbonization of non-alkali organic salts such as citrate salts of iron, zinc or calcium. The carbonized products contain numerous inorganic nanoparticles (i.e. Fe, ZnO or CaO) embedded within a carbonaceous matrix. These nanoparticles act as endotemplate, which when removed, leaves a mesoporous network. The resulting carbon samples have a large specific surface area up to ∼1600 m² g⁻¹ and a porosity made up almost exclusively of mesopores. An appropriate heat-treatment of these materials with melamine allows the synthesis of N-doped carbons which have a high nitrogen content (∼8–9 wt.%), a large specific surface area and retain the mesoporous structure. The mesoporous carbon samples were employed as electrode materials in supercapacitors. They exhibit specific capacitances of 200–240 F g⁻¹ in 1 M H₂SO₄ and 100–130 F g⁻¹ in EMImTFSI/AN. More importantly, the carbon samples possess a good capacitance retention in both electrolytes (>50% in H₂SO₄ and >80% in EMImTFSI/AN at 100 A g⁻¹) owing to their mesoporous structure which facilitates the penetration and transportation of ions.     

Residence time distribution analysis and optimization of photocatalysis of phenazopyridine using immobilized TiO2 nanoparticles in a rectangular photoreactor

Optimization of photocatalytic degradation of phenazopyridine (PhP) under UV light irradiation using immobilized TiO₂ nanoparticles was studied. The effect of operational parameters was investigated using response surface methodology (RSM). Maximum removal efficiency was achieved at the optimum conditions: initial drug concentration of 10 mg/L, UV light intensity of 47 W/m², flow rate of 200 mL/min, and reaction time of 150 min. The residence time distribution (RTD) analysis was studied to find the effect of flow rate on the drug removal efficiency. The tracer (PhP) pulse injection response was studied with UV–vis measurements and was used to prepare RTD curves.     

Graphene aerogels as a highly efficient counter electrode material for dye-sensitized solar cells

Graphene aerogels (GAs) prepared with an organic sol–gel process, possessing a high specific surface area of 814 m²/g and a high electric conductivity of 850 S/m, are applied as a counter electrode material for dye-sensitized solar cells (DSSCs). The performance of the GA as the counter electrode material is found to be dependent on its film thickness, with thicker films offering more surface areas for the involved catalytic reduction reaction but at the same time increasing the charge and mass transport resistances. At an optimum GA film thickness of 4.9 μm, a power conversion efficiency of 96% of that achieved with a Pt counter electrode based DSSC is obtained. In addition, a thinner GA film of 1.7 μm, when loaded with Pt of 1 mol% through a photo-reduction process, achieves a power conversion efficiency of 98% of that obtained with a Pt counter electrode based DSSC. The excellent performances of the GA-based counter electrodes are manifested with electrochemical impedance analyses and cyclic voltammetry based catalytic activity analyses.