Atomic layer deposition of TiO_(2) on carbon-nanotubes membrane for capacitive deionization removal of chromium from water

Chromium(Cr)is a common heavy metal that has severe impacts on the ecosystem and human health.Capacitive deionization(CDI)is an environment-friendly and energy-efficient electrochemical purification technology to remove Cr from polluted water.The performance of CDI systems relies primarily on the properties of electrodes.Carbon-nanotubes(CNTs)membranes are promising candidates in creating advanced CDI electrodes and processes.However,the low electrosorption capacity and high hydrophobicity of CNTs greatly impede their applications in water systems.In this study,we employ atomic layer deposition(ALD)to deposit TiO_(2) nanoparticulates on CNTs membranes for preparing electrodes with hydrophilicity.The TiO_(2)-deposited CNTs membranes display preferable electrosorption performance and reusability in CDI processes after only 20 ALD cycles deposition.The total Cr and Cr(VI)removal efficiencies are significantly improved to 92.1%and 93.3%,respectively.This work demonstrates that ALD is a highly controllable and simple method to produce advanced CDI electrodes,and broadens the application of metal oxide/carbon composites in the electrochemical processes.

Removal of Chromium from Chromium（VI） Solutions by Adsorption and Reduction Using Immobilized Persimmon Gel

The removal of chromium（Vl） from an aqueous solution using persimmon gel was examined. The amount of chromium（VI） removed was strongly affected by the pH of the solution, with all ehromium（VI） being removed at pH 2 or lower. However, in a solution containing, 15 mg dry weight of immobilized persimmon gel, the amount of removed chromium（VI） decreased as the pH increased. A part of chromium（VI） was reduced another oxidation stage, mainly chromium（III）, by immobilized persimmon gel. The amount of reduced chromium（III） in the solution was increased with decreasing the pH of the solution. As a result, the amount of total chromium removed was maximal at pH 2. The amount of chromium removed were affected by the chromium concentration and the amount of gel. The maximal amount of chromium removed by the column system was also discussed.

Comparative Study of Removal of Hexavalent Chromium from Water Using Metal Oxide Nanoparticles

Hexavalent chromium is one of the important heavy metals found in water and wastewater. The hexavalent form of chromium is considered to be a human carcinogen because of its mutagenic and carcinogenic properties. This work has focused on the comparison of copper oxide nanoparticles and aluminium oxide nanoparticles for the removal of chromium(VI) from water. The cooper oxide nanoparticles (CuNP) and aluminium oxide nanoparticles (AlNP) were synthesised by sol gel method. Both the adsorbents were evaluated for the adsorption capacity using Langmuir and Freundlich adsorption model. The CuNP and AlNP were characterized for X-ray diffraction and SEM. The study indicated that the AlNP showed better removal as compared to CuNP and can be further explored as potential adsorbent for hexavalent chromium removal.

Chromium Biosorption by Dried Biomass of Water Spinach （Ipomoea Aquatica）

Chromium is a toxic heavy metal that is widely used in industries such as metallurgical industries, and tannery industries. This study investigates the use of an alternative adsorption technology, biosorption, using dried biomass of water spinach （Ipomoea aquatica） in removing chromium from aqueous solutions. Dried biomass was prepared through washing, drying, cutting and alkali treatment. K,Cr207 solutions at an initial concentration of 200~ 14.72 mg/L were added to biomass weight of 200.0~ 1.1 mg at varying pH values of 1.00, 2.00, 3.00~0.02, 4.00~0.58 and 5.00~0.44. The maximum total chromium ion uptake was at pH=2, wherein the biomass adsorbed was 9.56~0.64 ppm Cr/mg biomass. K2Cr207 solutions at concentrations of 10.00~0.32, 50.00~0.95, 100.00~0.76, 200.00~4.82 and 300.00~4.69 mg/L were added to flasks with a biomass weight of 200.00~0.75 mg and pH of 2.00~0.25. The behavior of chromium ion biosorption unto the dried water spinach best fits the Langmuir isotherm with a coefficient of determination （R2） value of 0.9993. The calculated maximum adsorption （%） is 0.13889 kg/kg. The adsorption equilibrium constant （K） is 1705.83 mg/L. The continuous experiment showed that the kinetic behavior of the biomass in a packed bed column followed the following equation with a coefficient of determination （R2） value of 0.7039： C/C0=0.266e^-0.004t

Simultaneous removal of chromium and arsenate from contaminated groundwater by ferrous sulfate:Batch uptake behavior

Chromium and/or arsenate removal by Fe（Ⅱ） as a function of pH, Fe（Ⅱ） dosage and initial Cr（Ⅵ）/As（Ⅴ） ratio were examined in batch tests. The presence of arsenate reduced the removal efficiency of chromium by Fe（Ⅱ）, while the presence of chromate significantly increased the removal efficiency of arsenate by Fe（Ⅱ） at pH 6-8, In the absence of arsenate, chromium removal by Fe（Ⅱ） increased to a maximum with increasing pH from 4 to 7 and then decreased with a further increase in pH. The increment in Fe（Ⅱ） dosage resulted in an improvement in chromium removal and the improvement was more remarkable under alkaline conditions than that under acidic conditions. Chromium removal by Fe（Ⅱ） was reduced to a larger extent under neutral and alkaline conditions than that under acidic conditions due to the presence of 10 μtmol/L arsenate. The presence of 20 μmol/L arsenate slightly improved chromium removal by Fe（Ⅱ） at pH 3.9-5,8, but had detrimental effects at pH 6.7-9.8. Arsenate removal was improved significantly at pH 4-9 due to the presence of 10μmol/L chromate at Fe（Ⅱ） dosages of 20-60 μmol/L. Elevating the chromate concentration from 10 to 20μmol/L resulted in a further improvement in arsenate removal at pH 4.0-4.6 when Fe（Ⅱ） was dosed at 30-60 μmol/L.

Removal and desorption of chromium in synthetic effluent by a mixed culture in a bioreactor with a magnetic field

Two chromium removal experiments were performed in bioreactors with and without a magnetic field under the same conditions.The release of the chromium present in the biomass was tested in two experiments one with the initial pH of the medium and one with pH 4.0.The objective was to remove Cr(Ⅵ)and total Cr from the effluent,this was carried out by placing biological treatments of synthetic effluent contaminated with 100 mg/L of Cr(Ⅵ)in a bioreactor with neodymium magnets that applied a magnetic field(intensity85.4 mT)to the mixed culture.The removal of Cr(Ⅵ)was approximately 100.0%for the bioreactor with a magnetic field and 93,3%for the bioreactor without a magnetic field for9 hr of recirculation of the synthetic effluent by the bioreactor.The removal of total Cr was61.6%and 48.4%,with and without a magnetic field,respectively;for 24 hr.The desorption of Cr(VI)in the synthetic effluent was 0.05 mg/L,which is below the limit established by Brazilian legislation(0.1 mg/L)for the discharge of effluent containing Cr(Ⅵ)into bodies of water.The results obtained for the removal of chromium in synthetic effluent suggested that there was no significant influence on the viable cell count of the mixed culture.The desorption of Cr(Ⅵ)in synthetic effluent after bioadsorption of chromium by the mixed culture in the process of removal of chromium in bioreactors with and without a magnetic field was not significant in either of the experiments with different initial pHs.

Hyperbranched magnetic polymer:highly efficient removal of Cr(Ⅵ)and application in electroplating wastewater

By using a two-step hydrothermal method and trithiocyanuric acid(TTCA),2,4,6-trihydrazino-1,3,5-triazine(THT),and Fe_(3)O_(4)as raw materials,a spherical magnetic adsorbent polymer(TTCA/THT@Fe_(3)O_(4))was synthesized to achieve the efficient removal of Cr(VI)from wastewater.Under optimal adsorption conditions,the maximum adsorption capacity of TTCA/THT@Fe_(3)O_(4)for Cr(VI)can reach 1340 mg∙g‒1.Notably,the removal efficiency can approach 98.9%,even at the lower concentration of 20 mg∙L^(‒1)Cr(VI).For actual wastewater containing Cr(VI),the Cr(VI)concentration was reduced from 25.8 to 0.4 mg∙L^(‒1),a remarkable 20%lower than the current industry discharge standard value.A mechanism for the high adsorption performance of Cr(VI)on TTCA/THT@Fe_(3)O_(4)was investigated using Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy,and density functional theory.It can be plausibly attributed to the formation of Cr/N and Cr/S coordination bonds.Additionally,surface electrostatic adsorption,reduction effects,and the spherical polymer structure increase the contact area with Cr(VI),maximizing adsorption.The synergistic effect of adsorption and reduction enhances the adsorption performance of TTCA/THT@Fe_(3)O_(4)for Cr(VI)and total chromium in water.The resultant polymer has a simple preparation process,excellent adsorption performance,easy magnetic separation,and promising application for actual wastewater.

Construction of Ionic Porous Organic Polymers(iPOPs)via Pyrylium Mediated Transformation

Two new ionic porous organic polymers(iPOPs)with different counter anions were successfully fabricated via well-known pyrylium mediated transformation into pyridinium.13C solid-state NMR,XPS,and FTIR were analyzed and confirmed the formation of pyridinium in the network.Containing charged and aromatic networks,both iPOPs exhibit a high affinity towards toxic hexavalent chromium Cr(Ⅵ)ions.What is more,it has been demonstrated that both CO2 adsorption and Cr(Ⅵ)removal properties can be tuned by simply varying counter anions.