Bioremediation of Hexavalent Chromium Pollution by Sporosarcina saromensis M52 Isolated from Offshore Sediments in Xiamen, China

Objective Cr（VI） removal from industrial effluents and sediments has attracted the attention of environmental researchers. In the present study, we aimed to isolate bacteria for Cr（VI） bioremediation from sediment samples and to optimize parameters of biodegradation. Methods Strains with the ability to tolerate Cr（VI） were obtained by serial dilution and spread plate methods and characterized by morphology, 16 S r DNA identification, and phylogenetic analysis. Cr（VI） was determined using the 1,5-diphenylcarbazide method, and the optimum p H and temperature for degradation were studied using a multiple-factor mixed experimental design. Statistical analysis methods were used to analyze the results. Results Fifty-five strains were obtained, and one strain（Sporosarcina saromensis M52; patent application number： 201410819443.3） having the ability to tolerate 500 mg Cr（VI）/L was selected to optimize the degradation conditions. M52 was found be able to efficiently remove 50-200 mg Cr（VI）/L in 24 h, achieving the highest removal efficiency at p H 7.0-8.5 and 35 °C. Moreover, M52 could completely degrade 100 mg Cr（VI）/L at p H 8.0 and 35 °C in 24 h. The mechanism involved in the reduction of Cr（VI） was considered to be bioreduction rather than absorption. Conclusion The strong degradation ability of S. saromensis M52 and its advantageous functional characteristics support the potential use of this organism for bioremediation of heavy metal pollution.

Cytotoxicity and genome-wide microarray analysis of intestinal smooth muscle cells in response to hexavalent chromium induction

Chronic ingestion of high concentrations of hexavalent chromium[Cr(VI)]in drinking water induces intestinal tumors in mice;however,information on its toxicity on intestinal smooth muscle cells is limited.The present study aimed to assess the in vitro and in vivo toxicological effects of Cr(VI)on intestinal smooth muscle cells.Human intestinal smooth muscle cells(HISM cells)were cultured with different concentrations of Cr(VI)to evaluate effects on cell proliferation ability,oxidative stress levels,and antioxidant system.Furthermore,tissue sections in Cr(VI)exposed rabbits were analyzed to evaluate toxicity on intestinal muscle cells in vivo.Gene chips were utilized to assess differential gene expression profiles at the genome-wide level in 1μmol/L Cr(VI)treated cells.Intestinal tissue biopsy results showed that Cr(VI)increased the incidences of diffuse epithelial hyperplasia in intestinal jejunum but caused no obvious damage to the structure of the muscularis.Cell proliferation analysis revealed that high concentrations(≥64μmol/L)but not low concentrations of Cr(VI)(≤16μmol/L)significantly inhibited the growth of HISM cells.For oxidative stress levels,the expression of reactive oxygen species(ROS)and nitric oxide(NO)was elevated at high concentrations(≥64μmol/L)but not at low concentrations of Cr(VI)(≤16μmol/L).In addition,dose-dependent increases in the activity of oxidized glutathione(GSSH)/total-glutathione(T-GSH)were also observed.Gene chip screened 491 differentially expressed genes including genes associated with cell apoptosis,oxidations,and cytoskeletons.Some of these differentially expressed genes may be unique to smooth muscle cells in response to Cr(VI)induction.

Titanium dioxide-graphene composite electrochemical sensor for detection of hexavalent chromium

Hexavalent chromium(Cr(VI))compound is useful to various industries but is toxic and carcinogenic.In this research work,we fab-ricate an amperometric sensor for the determination of Cr(VI),using a titanium dioxide(TiO2)-reduced graphene oxide(rGO)composite as the sensing element.The composite was synthesized following sol−gel chemistry,yielding TiO2 nanoparticles of~50 nm in size,immobilized on chemically exfoliated rGO sheets.The composite was employed in a 3-electrode electrochemical cell and operated in an amperometric mode,exhibiting good responses to the 50 to 500 ppb Cr(VI).Our best result from pH 3 Mcilvane’s buffer medium reveals the sensitivity of 9.12×10−4 ppb−1 and a detection limit of 6 ppb with no signal interference from 200 ppm Ca(II),150 ppm Mg(II),and 50 ppb Pb(II).The excellent results of the TiO2-rGO sensor can be attributed to synergic effects between TiO2 and rGO,resulting from the presence of n-p heterojunctions and the formation of the TiO2 nanoparticles on rGO.

Anticlastogenic Effect of Redistilled Cow's Urine Distillate in Human Peripheral Lymphocytes Challenged With Manganese Dioxide and Hexavalent Chromium

Objective To study the anticlastogenic effect of redistilled cow＇s urine distillate （RCUD） in human peripheral lymphocytes （HLC） challenged with manganese dioxide and hexavalent chromium. Methods The anticlastogenic activity of redistilled cow＇s urine distillate was studied in human polymorphonuclear leukocytes （HPNLs） and human peripheral lymphocytes in vitro challenged with manganese dioxide and hexavalent chromium as established genotoxicants and clastogens which could cause induction of DNA strand break, chromosomal aberration and micronucleus. Three different levels of RCUD： 1 μL/mL, 50 μL/mL and 100 μL/mL, were used in the study. Results Manganese dioxide and hexavalent chromium caused statistically significant DNA strand break, chromosomal aberration and micronucleus formation, which could be protected by redisfilled cow＇s urine distillate. Conclusion The redistilled cow＇s urine distillate posseses strong anfigenotoxic and antielastogenic properties against HPNLs and HLC treated with Cr^＋6 and MnO2. This property is mainly due to the antioxidants present in RCUD.

Cytotoxicity and genome-wide microarray analysis of intestinal smooth muscle cells in response to hexavalent chromium induction

Chronic ingestion of high concentrations of hexavalent chromium [Cr（VI）] in drinking water induces intestinal tumors in mice; however, information on its toxicity on intestinal smooth muscle cells is limited. The present study aimed to assess the in vitro and in vivo toxicological effects of Cr（VI） on intestinal smooth muscle cells. Human intestinal smooth muscle cells （HISM cells） were cultured with different concentrations of Cr（VI） to evaluate effects on cell proliferation ability, oxidative stress levels, and antioxidant system. Furthermore, tissue sections in Cr（VI） exposed rabbits were analyzed to evaluate toxicity on intestinal muscle cells in vivo. Gene chips were utilized to assess differential gene expression profiles at the genome-wide level in 1 gmol/L Cr（VI） treated cells. Intestinal tissue biopsy results showed that Cr（VI） increased the incidences of diffuse epithelial hyperplasia in intestinal jejunum but caused no obvious damage to the structure of the muscularis. Cell proliferation analysis revealed that high concentrations （〉__64 gmol/L） but not low concentrations of Cr（VI） （〈16 ~tmol/L） significantly inhibited the growth of HISM cells. For oxidative stress levels, the expression of reactive oxygen species （ROS） and nitric oxide （NO） was elevated at high concentrations （〉64 pmol/L） but not at low concentrations of Cr（VI） （〈16 pmol/L）. In addition, dose-dependent increases in the activity of oxidized glutathione （GSSH）/total-glutathione （T-GSH） were also observed. Gene chip screened 491 differentially expressed genes including genes associated with cell apoptosis, oxidations, and cytoskeletons. Some of these differentially expressed genes may be unique to smooth muscle cells in response to Cr（VI） induction.

Determination of Hexavalent Chromium in Refractories by Diphenylcarbazide Spectrophotometry

The high chrome refractories were crushed,ground into powder and sampled.A mixture solution of sodium carbonate and sodium hydroxide was used to extract the powder samples.The extracted solution from the samples was mixed and reacted with diphenylcarbazide to form colored substance.The hexavalent chromium content in the samples was determined by spectrophotometry.The effects of the extracting conditions,the color reagent reaction conditions,the sample mass,the working curve and the trivalent chromium coexistence on the results were studied.The experiments about determination,recovery and precision were carried out.The relative standard deviation was less than 5%and the recovery rate was 98%-104%.

Flow-Injection Flame Atomic Absorption Determination of Hexavalent Chromium with On-Line Preconcentration on an Anion Imprinted Polymer

A flow injection preconcentration system for the flame atomic absorption spectrometric determination of hexavalent chromium has been developed. The method employs on-line preconcentration of Cr(VI) on a minicolumn packed with Cr(VI)-imprinted poly(4-vinyl pyridineco-2-hydroxyethyl methacrylate) placed into a flow injection system. Hexava-lent chromium was eluted with a small volume of diluted hydrochloric acid into the nebulizer-burner system of a flame atomic absorption spectrometer. An enrichment factor of 550 and a 3σ detection limit of 0.04 μg·L-1 along a sampling frequency of 4 h-1 at a sample flow rate of 3.5 mL·min-1. The relative standard deviation is 2.9% for 1 μg·L-1 Cr(VI) (n = 11). The flow injection system proposed has the advantage of being simpler because the use of expensive and sophisticated instruments is avoided. Ease of use, continuous process and selectivity make this method suitable for Cr(VI) determination in different environmental samples such as sea and river waters, soils and sediments.

Electroreduction of hexavalent chromium using a porous titanium flow-through electrode and intelligent prediction based on a back propagation neural network

Flow-through electrodes have been demonstrated to be effective for electroreduction of Cr(VI),but shortcomings are tedious preparation and short lifetimes.Herein,porous titanium available in the market was studied as a flow-through electrode for Cr(VI)electroreduction.In addition,the intelligent prediction of electrolytic performance based on a back propagation neural network(BPNN)was developed.Voltametric studies revealed that Cr(VI)electroreduction was a diffusion-controlled process.Use of the flow-through mode achieved a high limiting diffusion current as a result of enhanced mass transfer and favorable kinetics.Electroreduction of Cr(VI)in the flow-through system was 1.95 times higher than in a parallel-plate electrode system.When the influent(initial pH 2.0 and 106 mg/L Cr(VI))was treated at 5.0 V and a flux of 51 L/(h·m2),a reduction efficiency of~99.9%was obtained without cyclic electrolysis process.Sulfate served as the supporting electrolyte and pH regulator,as reactive CrSO72−species were formed as a result of feeding HSO4−.Cr(III)was confirmed as the final product due to the sequential three-electron transport or disproportionation of the intermediate.The developed BPNN model achieved good prediction accuracy with respect to Cr(VI)electroreduction with a high correlation coefficient(R2=0.943).Additionally,the electroreduction efficiencies for various operating inputs were predicted based on the BPNN model,which demonstrates the evolutionary role of intelligent systems in future electrochemical technologies.

Efficient reduction of hexavalent chromium with microscale Fe/Cu bimetals:Efficiency and the role of Cu

Microscale zero valent iron(mFe^(0))is one of the most potential water pollution remediation materials,but the effective utilization ability of electrons released by mFe^(0)in the reduction of hexavalent chromium(Cr(VI))is not satisfactory.Here,we find the microscale iron-copper(m Fe/Cu)bimetals coated with copper on the surface of mFe^(0)can significantly improve the effective utilization of electrons released by mFe^(0).Electrochemical analysis displays that copper plating on the surface of m Fe/Cu can promote the release the electrons from mFe^(0)and reduce the impedance of mFe^(0).Spin-polarized density functional theory(DFT)calculation reveals that Cu on the surface of m Fe/Cu bimetals promotes the release of electrons from mFe^(0)and reduces the adsorption energy of Fe to Cr.As the electron transporter,moreover,Cu can always attract Cr to the hollow position near itself of the Fe surface,which could promote the effective utilization of electrons released by Fe.Effective utilization ability of electrons in m Fe/Cu system is 12.5 times higher than that in mFe^(0)system.Our findings provide another basis for the efficient reduction of Cr(VI)by m Fe/Cu bimetals,which could promote the application and popularization of m Fe/Cu bimetals.

Nanoencapsulation of hexavalent chromium with nanoscale zero-valent iron:High resolution chemical mapping of the passivation layer

Solid phase reactions of Cr（Ⅵ） with Fe（0） were investigated with spherical-aberration-corrected scanning transmission electron microscopy（Cs-STEM） integrated with X-ray energy-dispersive spectroscopy（XEDS）. Near-atomic resolution elemental mappings of Cr（Ⅵ）–Fe（0） reactions were acquired. Experimental results show that rate and extent of Cr（Ⅵ） encapsulation are strongly dependent on the initial concentration of Cr（Ⅵ） in solution. Low Cr loading in nZⅥ（〈1.0 wt%） promotes the electrochemical oxidation and continuous corrosion of n ZⅥ while high Cr loading（〉1.0 wt%） can quickly shut down the Cr uptake. With the progress of iron oxidation and dissolution, elements of Cr and O counter-diffuse into the nanoparticles and accumulate in the core region at low levels of Cr（Ⅵ）（e.g., 〈 10 mg/L）. Whereas the reacted n ZⅥ is quickly coated with a newly-formed layer of 2–4 nm in the presence of concentrated Cr（Ⅵ）（e.g., 〉 100 mg/L）. The passivation structure is stable over a wide range of pH unless pH is low enough to dissolve the passivation layer. X-ray photoelectron spectroscopy（XPS） depth profiling reconfirms that the composition of the newly-formed surface layer consists of Fe（Ⅲ）–Cr（Ⅲ）（oxy）hydroxides with Cr（Ⅵ） adsorbed on the outside surface. The insoluble and insulating Fe（Ⅲ）–Cr（Ⅲ）（oxy）hydroxide layer can completely cover the n ZⅥ surface above the critical Cr loading and shield the electron transfer. Thus, the fast passivation of nZⅥ in high Cr（Ⅵ） solution is detrimental to the performance of nZⅥ for Cr（Ⅵ） treatment and remediation.

Bioreduction of hexavalent chromium:Effect of compost-derived humic acids and hematite

Composting can enhance the nutrie nt ele ments cycling and reduce carbon dioxide production.However,little information is available regarding the application of compost for the remediation of the contaminated soil.In this study,we assess the response of the redox capacities(electron accepting capacities(EAC)and electron donating capacities(EDC))of compost-derived humic acids(HAs)to the bioreduction of hexavalent chromium(Cr(Ⅵ)),especially in presence of hematite.The result showed that the compost-derived HAs played an important role in the bioreduction of Cr(Ⅵ)in presence and absence of hematite under the anoxic,neutral(pH 7)and motionless conditions.Based on the pseudo-first order kinetic model,the rate constants of Cr(Ⅵ)reduction increased by 1.36-2.0 times when compost-derived HAs was added.The redox capacity originating from the polysaccharide structure of compost-derived HAs made them effective in the direct Cr(Ⅵ)reduction(without MR-1)at pH 7.Meanwhile,the reduction rates were inversely proportional to the composting treatment time.When iron mineral(Fe_(2)O_(3))and compost-derived HAs were both present,the rate constants of Cr(Ⅵ)reduction increased by 2.35-5.09,which were higher than the rate of Cr(Ⅵ)reduction in HA-only systems,indicating that the hematite played a crucial role in the bioreduction process of Cr(Ⅵ).EAC and quinonoid structures played a major role in enhancing the bioreduction of Cr(Ⅵ)when iron mineral and compost-derived HAs coexisted in the system.The results can extend the application fields of compost and will provide a new insight for the remediation of Cr(Ⅵ)-contaminated soil.

Kinetics and mechanism of hexavalent chromium removal by basic oxygen furnace slag

Basic oxygen furnace slag（BOFS） has the potential to remove hexavalent chromium（Cr（VI））from wastewater by a redox process due to the presence of minerals containing Fe2＋. The effects of the solution p H, initial Cr（VI） concentration, BOFS dosage, BOFS particle size, and temperature on the removal of Cr（VI） was investigated in detail through batch tests. The chemical and mineral compositions of fresh and reacted BOFS were characterized using scanning electron microscope（SEM） equipped with an energy dispersive spectrometer（EDS）system and X-ray diffractometer（XRD）. The results show that Cr（VI） in wastewater can be efficiently removed by Fe2＋released from BOFS under appropriate acidic conditions. The removal of Cr（VI） by BOFS significantly depended on the parameters mentioned above. The reaction of Cr（VI） with BOFS followed the pseudo-second-order kinetic model. Fe2＋responsible for Cr（VI） removal was primarily derived from the dissolution of Fe O and Fe3O4 in BOFS. When H2SO4 was used to adjust the solution acidity, gypsum（Ca SO4·2H2O）could be formed and become an armoring precipitate layer on the BOFS surface, hindering the release of Fe2＋and the removal of Cr（VI）. Finally, the main mechanism of Cr（VI） removal by BOFS was described using several consecutive reaction steps.

Kinetics of hexavalent chromium reduction by iron metal

The kinetics of Cr(VI)reduction to Cr(III)by metallic iron(Fe0)was studied in batch reactors for a range of reactant concentrations,pH and temperatures.Nearly 86.8%removal efficiency for Cr(VI)was achieved when Fe0 concentration was 6 g/L(using commercial iron powder(<200 mesh)in 120 min).The reduction of hexavalent chro-mium took place on the surface of the iron particles following pseudo-first order kinetics.The rate of Cr(VI)reduction increased with increasing Fe0 addition and temperature but inversely with initial pH.The pseudo-first-order rate coeffi-cients(kobs)were determined as 0.0024,0.010,0.0268 and 0.0628 min−1 when iron powder dosages were 2,6,10 and 14 g/L at 25°C and pH 5.5,respectively.According to the Arrehenius equation,the apparent activation energy of 26.5 kJ/mol and pre-exponential factor of 3330 min−1 were obtained at the temperature range of 288−308 K.Different Fe0 types were compared in this study.The reactivity was in the order starch-stabilized Fe0 nanoparticles>Fe0 nano-particles>Fe0 powder>Fe0 filings.Electrochemical analysis of the reaction process showed that Cr(III)and Fe(III)hydroxides should be the dominant final products.

Robust Fe^(2+)-doped nickel-iron layered double hydroxide electrode for electrocatalytic reduction of hexavalent chromium by pulsed potential method

Electrocatalytic reduction of Cr(Ⅵ)to less toxic Cr(Ⅲ)is deemed as a promising technique.Conventional electrocatalytic reduction is always driven by a constant cathodic potential,which exhibits a repelling action to Cr(Ⅵ)oxyanions in wastewater and consequently suppresses reduction kinetics.In order to remarkably accelerate Cr(Ⅵ)electrocatalytic reduction,we applied a pulsed potential on an Fe^(2+)-NiFe LDH/NF electrode synthesized by in situ growth of Fe^(2+)-doped NiFe LDH nanosheets on Ni foam using a spontaneous redox reaction.Under anodic potential section,HCrO_(4)^(–) anions are adsorbed on the electrode surface and reduced to Cr(Ⅲ)by Fe^(2+).Then,Cr(Ⅲ)ions are desorbed from the electrode surface under coulombic force.The regeneration of Fe^(2+) and direct reduction of Cr(Ⅵ)are achieved under cathodic potential section.The pulsed potential can achieve complete elimination of Cr(Ⅵ)within 60 min at an initial concentration of 10 mg L^(-1),and the removal efficiency shows a 60%increase with respect to that under constant cathodic potential.

Effect of Ti（lll） Surface Defects on the Process of Photocatalytic Reduction of Hexavalent Chromium

In this paper, the process of photocatalytic reduction of hexavalent chromium was investigated over Ti3＋- modified TiO2 photocatalysts. The Ti3＋ surface defects were repaired by annealing as-prepared sample at different temperatures to control the amount of Ti3＋ sites. The samples were characterized by SEM, XRD, BET, UV-Vis absorption, EPR and XPS. The results showed Ti3＋ defects were successfully doped in TiO2. The surface selective adsorption of hexavalent chromium [Cr2072 （Cr（VI））] and the desorption of trivalent chromium [Cr3＋ （Cr（III））] were investigated during the process ofphotocatalytic reduction positive charges due to more Ti3＋ defects on the surface show a Accordingly, the surface positive reduction of Cr（VI）. charges controlled by the Ti3＋ Zeta potential results presented that the increased significant improvement for adsorption of Cr（VI）. defects play important roles in the photocatalytic

Reduction of hexavalent chromium with scrap iron in a fixed bed reactor

The reduction of hexavalent chromium by scrap iron was investigated in continuous long-term fixed bed system. The effects of pH, empty bed contact time （EBCT）, and initial Cr（VI） concentration on Cr（VI） reduction were studied. The results showed that the pH, EBCT, and initial Cr（VI） concentration significantly affected the reduction capacity of scrap iron. The reduction capacity of scrap iron were 4.56, 1.51, and 0.57mg Cr（VI）-g1 Fe0 at pH 3, 5, and 7 （initial Cr（VI） concentration 4 mg.L 1, EBCT 2 min, and temperature 25℃）, 0.51, 1.51, and 2.85 mg Cr（VI）.g-I Fe0 at EBCTs of 0.5, 2.0, and 6.0rain （initial Cr（VI） concentration 4mg.L-1, pH 5, and temperature 25℃）, and 2.99, 1.51, and 1.01 mg Cr（VI）. gl Fe0 at influent concentrations of 1, 4, and 8 mg.L ^-1（EBCT 2 min, pH 5, and temperature 25℃）, respectively. Fe（total） concentration in the column effluent continuously decreased in time, due to a decrease in time of the iron corrosion rate. The fixed bed reactor can be readily used for the treatment of drinking water containing low amounts of Cr（VI） ions, although the hardness and humic acid in water may shorten the lifetime of the reactor, the reduction capacity of scrap iron still achieved 1.98 mg Cr6 ＋- g-~ Fe. Scanning electron micro- scope equipped with energy dispersion spectrometer and X-ray diffraction were conducted to examine the surface species of the scrap iron before and after its use. In addition to iron oxides and hydroxide species, iron-chromium complex was also observed on the reacted scrap iron.

Palladium nanoparticles supported on amine-functionalized glass fiber mat for fixed-bed reactors on the effective removal of hexavalent chromium by catalytic reduction

Palladium nanoparticles were deposited on the amine-grafted glass fiber mat （GFM-NH2） catalyst support by a conventional impregnation process followed by the borohydride reduction in aqueous solution at room temperature to create the designed Pd/GFM-NH2 catalyst. By the use of large size glass fiber mat without nano/mesopores as the catalyst support, the internal mass transfer limitations due to the existence of nano/mesopores on the catalyst support were eliminated and the Pd/GFM-NH2 catalyst could be easily separated from treated water due to the large size of the catalyst support. Batch experiments demonstrate its good catalytic reduction performance of Cr（VI） with formic acid as the reducing agent. It also demonstrated an efficient Cr（VI） removal and stability in a lab-prepared, packed fixed-bed tube reactor for the continuous treatment of Cr（VI）-containing water. Thus, it has a good potential for the catalytic reduction of Cr（VI） in the water treatment practice.

Reactions of Chromium during the Calcination of Cement Clinker Produced Using Steel Slag

We investigated the effects of calcination temperature(950-1450℃),steel slag content,and the total chromium content of steel slag on the Cr^(6+)contents of clinker samples produced using steel slags with different chromium contents.Additionally,the reactions of chromium in clinker(produced using steel slag)during calcination were studied.It is found that Cr^(6+)conversion increases with increasing calcination temperature to 1250℃,reaching a maximum of 43%-79%,before decreasing to 18%-42%at 1450℃.Cr^(6+)is mainly formed by the oxidation of trivalent chromium(Cr^(3+))during the solid-phase reaction stage of clinker calcination.Furthermore,the Cr^(6+)content of a clinker sample is proportional to the chromium content of its raw meal precursor and is mainly in the form of water-insoluble calcium chromate(CaCrO_(4)).The chromium in clinker is mainly distributed in tricalcium aluminate and tetracalcium aluminoferrite,however,some is present in silicate minerals.We expect to inform the monitoring and control of the Cr^(6+)content of clinker(produced using steel slag)and resulting cement.

Efficient removal of Cr(VI) by polydopamine-modified lignin from aqueous solution: Batch and XAFS studies

Lignocellulose has the potential to become a bio-based adsorbent due to its biodegradability and renewability.In this study,a novel polydopamine functionalized-lignin(lignin@PDA),prepared via self-polymerization of dopamine(PDA)on lignin,was used as a bio-based adsorbent for rapid scavenging of hexavalent chromium(Cr(VI)).The morphology,functional groups,crystalline structure,and chemical composition of lignin@PDA were characterized with a scanning electron microscope-energy dispersive spectrometer,Fourier transform infrared spectroscopy,X-ray diffraction,and X-ray photoelectron spectroscopy.The Cr(VI)adsorption process of lignin@PDA was studied using batch experiments as a function of pH,ionic strength,adsorbent dose,and contact time at room temperature.The adsorption rate of lignin@PDA was five times greater than that of the unmodified lignin,with a maximum adsorption capacity of 102.6 mg/g in an acidic medium.The adsorption of Cr(VI)on lignin@PDA fit the pseudo-secondorder equation and the Freundlich model,indicating that the adsorption process was mainly dominated by chemisorption and surface complexation.The thermodynamic parameters showed that adsorption of Cr(VI)on lignin@PDA was an endothermic and spontaneous process.The X-ray absorption fine structure results showed that sorption and reduction of Cr(VI)into Cr(II)occurred simultaneously on lignin.Moreover,PDA coating not only improved the reactivity of lignin but also promoted the complete reduction of Cr(VI)by lignin.According to these results,polydopamine functionalized-lignin is a promising bio-based adsorbent for immobilization of Cr(VI)from wastewater.

Amination of biochar surface from watermelon peel for toxic chromium removal enhancement

Watermelon peel residues were used to produce a new biochar by dehydration method.The new biochar has undergone two methods of chemical modification and the effect of this chemical modification on its ability to adsorb Cr(VI)ions from aqueous solution has been investigated.Three biochars,Melon-B,Melon-BO-NH_(2) and Melon-BO-TETA,were made from watermelon peel via dehydration with 50%sulfuric acid to give Melon-B followed by oxidation with ozone and amination using ammonium hydroxide to give Melon-BO-NH_(2) or Triethylenetetramine(TETA)to give Melon-BO-TETA.The prepared biochars were characterized by BET,BJH,SEM,FT-IR,TGA,DSC and EDAX analyses.The highest removal percentage of Cr(VI)ions was 69%for Melon-B,98%for Melon-BO-NH_(2) and 99%for Melon-BO-TETA biochars of 100 mg·L^(−1) Cr(VI)ions initial concentration and 1.0 g·L^(−1) adsorbents dose.The unmodified biochar(Melon-B)and modified biochars(Melon-BO-NH_(2) and Melon-BO-TETA)had maximum adsorption capacities(Q_(m))of 72.46,123.46,and 333.33 mg·g^(−1),respectively.The amination of biochar reduced the pore size of modified biochar,whereas the surface area was enhanced.The obtained data of isotherm models were tested using different error function equations.The Freundlich,Tempkin and Langmuir isotherm models were best fitted to the experimental data of Melon-B,Melon-BO-NH_(2) and Melon-BO-TETA,respectively.The adsorption rate was primarily controlled by pseudo-second–order rate model.Conclusively,the functional groups interactions are important for adsorption mechanisms and expected to control the adsorption process.The adsorption for the Melon-B,Melon-BO-NH_(2) and Melon-BO-TETA could be explained for acid–base interaction and hydrogen bonding interaction.