Initial Cr Concentration Research Articles

Adsorption of Cr(VI) from aqueous solution using mesoporous metal-organic framework-5 functionalized with the amino acids: Characterization, optimization, linear and nonlinear kinetic models

In the past decades, an extensive effort has been devoted to remove Hexavalent chromium H(Cr (VI)) from industrial effluents, owning to its great health concerns to humans and the environment. Recently, Metal organic framework (MOFs) adsorbents draws more attention of researchers to remove contaminants from aqueous environments in the recent years. In the present study, solvothermal method was employed to fabricate MOF-5 that was examined for Cr (VI) adsorption from water matrices. XRD, FESEM, EDS, FTIR and BET analyses were utilized to characterize MOF-5. The influence of some independent parameters on MOF-5 performance in Cr (VI) adsorption was explored in a batch mode system. It was found that the uptake rate of Cr (VI) is significantly affected by initial pH of solution; the maximum adsorption rate is favored by acidic pH. Also, the adsorption efficiency shows a direct relationship with contact time and adsorbent dose, and an indirect relation with initial Cr (VI) concentration. The adoption process was modeled and optimized successfully by two approach of response surface methodology and artificial neutral network approaches; both models indicated an accuracy of predictions by determining error distribution and statistical significance and a good fit to experimental data. The experimental data showed a superior agreement with linear and nonlinear Langmuir isotherm, as compared with the other isotherm models, and pseudo-second-order kinetic better described Cr (VI) adsorption data by MOF-5, compared to the other kinetic models. The maximum absorption capacity was 78.12 mg/g. Thermodynamic studies revealed that adsorption is spontaneous and endothermic process. The findings claimed the great reusability and high stability of MOF-5; adsorption efficiency decreased only by 92.4% after ten recycles. The interfering anions affected negatively on the adsorption efficiency in the order of phosphate > sulfate > chloride > nitrate. The present study provides valuable and good information for Cr (VI) adsorption on MOF-5 in water matrices.

Sustainable preparation of Fe(OH)3 and α-Fe2O3 nanoparticles employing Acacia catechu extract for efficient removal of chromium (VI) from aqueous solution

Indiscriminate disposal of industrial effluents containing undesired polyvalent metal ions such as Cr(III) and Cr(VI) into water bodies causes serious threat to public health and ecosystem. Therefore, it is necessary to develop new and sustainable methods for the efficient removal of such ions from water. Herein, iron hydroxide, Fe(OH)3, nanoparticles (NPs), have been prepared employing an aqueous extract of Acacia catechu leaves as green reducing as well as stabilizing agent. The annealing of Fe(OH)3 NPs results in the formation of highly crystalline α-Fe2O3 NPs. Thus prepared Fe(OH)3 and α-Fe2O3 NPs have been characterized for crystallinity, shape, size and porosity and tested for adsorptive removal of Cr(VI) from aqueous solution at varying pH, dose of NPs and initial concentration of Cr(VI). Removal efficacy of both forms of NPs (Fe(OH)3 and α-Fe2O3) towards Cr(VI) has been correlated with their structural aspects. Under optimal conditions, Fe(OH)3 NPs and α-Fe2O3 NPs have been found to remove 84.9 % and 22 % of Cr(VI) from aqueous solutions. The presence of surface –OH groups of polyols and that of NPs are assigned to be responsible for adsorption of Cr(VI) ions from aqueous solution. The maximum monolayer adsorption capacity of Fe(OH)3 NPs for Cr(VI), calculated from Langmuir isotherm is 29.5 mg g−1 at pH = 2 and 25 °C. It is expected that the present study would highlight the importance of the presence of bio-based templates on the surface of NPs for efficient removal of metal ions from aqueous solution.

Synergistic roles of Fe(II) on simultaneous removal of hexavalent chromium and trichloroethylene by attapulgite-supported nanoscale zero-valent iron/persulfate system

Synthesized attapulgite-supported nanoscale zero-valent iron (AT-nZVI) composite/persulfate (PS) systems were utilized to simultaneously remove hexavalent chromium (Cr(VI)) and trichloroethylene (TCE) from aqueous solutions. The structures of AT-nZVI before and after the reaction with Cr(VI)-TCE were characterized by TEM-EDS-Mapping, HR-TEM and HR-XPS with ion sputtering. The effects of initial Cr(VI), TCE and PS concentrations, and PS addition time intervals on Cr(VI)-TCE removal efficiencies were evaluated. Experimental results revealed that the AT-nZVI composites with 1 mM PS can effectively and simultaneously remove Cr(VI) and TCE with the removal efficiencies of Cr(VI) and TCE reaching 90.02% and 90.40% respectively. It is thought that PS promoted TCE oxidation and the reduction of Cr(VI), which was predominately controlled by Fe(II). TCE was mainly degraded by free radical oxidation resulting from the PS activation of AT-nZVI. The enhanced Cr(VI) removal was attributed to the exposed areas and available active sites of nZVI, and Fe(II) in the solution increased by PS-mediated processes of rapid corrosion and dissolution of nZVI. The dual roles of AT-nZVI as a activator for PS activation and reductant for Cr(VI) reduction in Cr(VI)-TCE removal were identified. This implies that AT-nZVI/PS can be utilized as potential remediation reagents for simultaneous removal of heavy metal and chlorinated solvents in groundwater frequently encountered in contaminated sites.

Leveraging the biosorption potential of Leptolyngbya boryana for Cr (VI) removal from aqueous solution

The present study attempts to utilize the cyanobacterial species, Leptolyngbya boryana, isolated from tannery effluent contaminated site for hexavalent chromium (Cr (VI)) removal from the aqueous solution. The isolated Leptolyngbya boryana showed efficient Cr (VI) removal along with potential tolerance ability even at higher concentrations. A Box-Behnken design of experiments was employed for optimizing and evaluating the effect of various parameters onto Cr (VI) removal. During the adsorption process, effect of adsorbent dose, initial Cr (VI) concentration and temperature played the key role. Further, the experiments were up-scaled to bioreactor level with all the optimized parameters for Cr (VI) removal. Interestingly, at the batch bioreactor level a slight decline in the removal efficiency was observed. The cyanobacterial species depicted a good tolerance limit (750 mg/L) even at higher concentration of Cr (VI). The maximum removal of 96.6% was obtained via the isolated cyanobacterial species depicting its potential for the heavy metal removal from the wastewater.

Sustainable Chromium Recovery From Wastewater Using Mango and Jackfruit Seed Kernel Bio-Adsorbents.

Wastewater is a rich source of valuable chemicals of industrial importance. However, their economic recovery is crucial for sustainability. The objective of the present work is to recover hexavalent chromium (Cr VI) as a value-added transition metal from wastewater cost-effectively; the biosorbent derived from seed kernels of mango (M) and jackfruit (JF) were applied for removing the metal from simulated wastewater. The functional groups of the biomass were analysed with the help of Fourier transform infrared (FTIR) spectroscopy, micrographs were generated using a scanning electron microscope, and crystallinity was determined by an x-ray diffractometer (XRD). The concentration of Cr VI in wastewater was analysed by an inductively coupled plasma optical emission spectrometer (ICP-OES). Process parameters (pH, dose, contact time, temperature, and initial concentration) were optimized for efficient Cr VI adsorption using a response surface methodology-based Box–Behnken design (BBD) employing Design-software 6.0.8. The batch experiment at room temperature at pH 4.8 and Cr VI removal ∼94% (M) and ∼92% (JF) was achieved by using a 60-mg dose and an initial Cr (VI) concentration of 2 ppm in 120 min. The equilibrium Cr binding on the biosorbent was well explained using Freundlich isotherm (R2 = 0.97), which indicated the indirect interactions between Cr (VI) and the biosorbent. Biosorption of Cr (VI) followed the pseudo-order and intra-particle diffusion models. The maximum adsorption capacity of the M and JF bio-adsorbent is 517.24 and 207.6 g/mg, respectively. These efficient, cost-effective, and eco-friendly biosorbents could be potentially applied for removing toxic Cr (VI) from polluted water.

Green treatment of chromium contaminated water using Spongomorpha indica

The current study presents chromium (VI) biosorption performance of Spongomorpha indica from synthetic medium. Spongomorpha indica, naturally available green marine alga was selected as an adsorbent. The influence of three process parameters i.e., initial pH, initial chromium (VI) ions concentration and Spongomorpha indica biomass dosage, on the performance of biosorbent was studied. CCD of RSM was adopted to optimize process parameters and the results were analyzed using ANOVA to determine significance of influential parameters and their interaction effect on process efficiency. The predicted optimum values i.e., the biosorption 95.29%, pH 5.62, initial Cr(VI) concentration 31.82 mg/L and Spongomorpha indica biomass dosage 0.04 g/L through statistical optimization were found to be approximately equal to the confirmation experiment measured values. The results of kinetic studies revealed that the mechanism involved in metal capturing by biosorbent is ionic interaction between metal cations and various surface ionic groups of biomass with heterogeneous mass transfer. Equilibrium isotherm studies disclosed that Langmuir model was well correlated to equilibrium data. FTIR and SEM analysis were recorded for surface characterization of Spongomorpha indica.

Reactivation of Passivated Biochar/Nanoscale Zero-Valent Iron by an Electroactive Microorganism for Cooperative Hexavalent Chromium Removal and Mechanisms

Nanoscale zero-valent iron (nZVI) shows excellent reduction of Cr(Ⅵ), but the passivation on its outer surface can restrict its longevity and performance. To tackle this problem, this work introduced Shewanella oneidensis MR-1, a dissimilatory iron-reducing bacterium, into the chemical reduction system of aged nZVI/biochar (B) and Cr(Ⅵ). The potential synergistic effect of Cr(Ⅵ) reduction of aged nZVI/B and MR-1 was systematically investigated under varying conditions. The results indicated that aged nZVI/B and MR-1 exhibited a synergistic effect at a pH of 7, and the removal rate of Cr(Ⅵ) increased by 51.3%. Further research showed that the synergistic effect could be attenuated with the increase in the initial Cr(Ⅵ) concentration and enhanced with the increase in the MR-1 concentration. The XPS spectra confirmed that Cr(Ⅵ) was mainly removed through reduction. The dissimilatory iron-reducing ability of MR-1 played a key role in enhancing the Cr(Ⅵ) reduction. The reductive dissolution of the oxidation layers not only released reactive sites inside the nZVI, but also reduced Cr(Ⅵ) by producing ferrous ions. Moreover, B promoted the reduction by dispersing the nZVI and mediating the extracellular electron transfer. This study provides a new insight into solving the passivation problem of the long-term application of nZVI for Cr(Ⅵ) removal, which is considered a promising solution for synergistically improving the performance of nZVI in environmental remediation.

Removal of hexavalent chromium ions and Acid Red 18 by superparamagnetic CoFe2O4/polyaniline nanocomposites under external ultrasonic fields

In the present research, the adsorptive removal of dye and Cr(VI) ions from the aquatic solutions have been investigated using fabricated magnetic cobalt ferrite (CoFe 2 O 4 ) nanoparticles coated by polyaniline (CoFe 2 O 4 /PANI) via a hydrothermal and in-situ polymerization method. Magnetic composite of CoFe 2 O 4 /PANI was characterized by FE-SEM, EDS, XRD, VSM, FTIR, BET, BJH, and element mapping. The resulting composite was applied for the removal of hexavalent chromium (Cr(VI)) ions and Acid Red 18 (AR18) anionic azo dye individually from an aqueous solution under external ultrasonic fields. The removal efficiency of Cr(VI) ions and AR18 dye were studied as functions of the various parameters like time sonication, amount of adsorbent, initial concentration of Cr(VI) or AR18, and solution pH. The adsorption behavior and the equilibrium data were represented by the Langmuir isotherm model. The maximum monolayer adsorption capacity by as-prepared composite reached 103.11 mg g −1 and 172.41 mg g −1 for Cr(VI) ions and AR18 dye, respectively. The thermodynamic analysis demonstrated that these adsorption processes were spontaneous in nature and endothermic. The magnetically recyclable composite indicated suitable reusability during cyclic adsorption. The increase in ionic strength causes a decrease in the adsorption of Cr(VI) and AR18. This study may provide a promising magnetic composite for the efficient removal of inorganic and organic anions from the water environment. • Application of magnetic CoFe 2 O 4 /PANI for ultrasound assisted adsorption of Cr(VI) ions and AR18 dye. • Desirability function approach combined with CCD method was used to optimize the process variables. • CoFe 2 O 4 /PANI is superior to CoFe 2 O 4 for Cr(VI) ions and AR18 dye adsorption. • The maximum adsorption capacity for Cr(VI) ions and AR18 dye reached 103.11 mg g −1 and 172.41 mg g −1 , respectively. • Reusability tests indicated suitable regenerability of CoFe 2 O 4 /PANI.

Assessment of algal biomass towards removal of Cr(VI) from tannery effluent: a sustainable approach.

The current investigation focuses on a systematic study of application of two dried algal biomass (i.e., Nostoc sp. and Turbinaria vulgaris) in removal of Cr(VI) from synthetic solution as well as tannery industrial wastewater. The optimized conditions for Cr(VI) removal are nearly same for the both the biosorbents (i.e., pH 2.8, initial Cr(VI) concentration 100 mg L-1, biomass dosage of 1.2g L-1, contact time 120 and 110 min). Nostoc sp. (qmax=23.94mg g-1) was observed to possess a superior removal capability when compared to Turbinaria vulgaris (qmax=21.8mg g-1). Desorption studies were performed with four different desorbing agents. Application study was conducted using tannery wastewater with Nostoc sp. and 94.20% removal of Cr(VI) was obtained. Hence, this study revealed that Nostoc sp. and T. vulgaris both have great potential to be an environment friendly and economic biosorbent for removal of Cr(VI) containing industrial effluent.

Impacts of Mixing Mode on Photocatalytic Reduction of Hexavalent Chromium over Titanium Dioxide Nanomaterial under Various Environmental Conditions

This study explores the effects of initial Cr(VI) concentration, wavelength, hole-scavenger (absence and presence of salicylic acid), and oxygen conditions (aeration by air, nitrogen gas, and mechanical stir only) on photocatalytic reduction of hexavalent chromium over titanium dioxide photocatalyst and the chromic species distribution after photocatalysis. The experimental results show the existence of strong interactions between these factors. The factor of hole-scavenger was more important than the UV light wavelength condition for a reduction of 3 mg Cr(VI) L−1, whereas both factors became important when Cr(VI) concentration increased to 20 mgL−1. The higher the UV wavelength was, the less the amount of chromium retained on the TiO2 surface. The influence of oxygen-containing conditions in the solution on the reduction of 3 mgL−1 Cr(VI) was unobvious, whereas its influence became remarkable for the reduction of 20 mgL−1 Cr(VI) in the presence of SA. The interaction between oxygen-containing factor and other environmental factors, such as Cr(VI) concentration and scavenger presence (SA in this study), is a key factor about the degree of oxygen effect on Cr(VI) photo-reduction and the chromic species distribution. Simple stirring obtained better photocatalytic efficiency than aeration by air or nitrogen gas.

Heavy metal removal of solid waste source sulphoaluminate cement with graphene oxide

Heavy metal pollution is one of the most severe issues facing the environment for its persistent and stable physicochemical property. This research demonstrated that, ettringite crystal phase -- main hydration product of solid waste source sulphoaluminate cement (WSAC), has a highly efficient heavy metal removal via cation exchange. Meanwhile, due to large specific surface area, rich functional groups, good adsorption performance for heavy metals and ability to promote the growth of ettringite crystal, graphene oxide (GO) was selected to further improve the solidification effect of WSAC towards heavy metals. The heavy metal ion adsorption effects on the WSAC, including to theadsorbent dosage, solution pH, adsorption time, initial Cr(III) concentration, adsorption temperature, and competitive adsorption for multiple heavy metal ions, were systematically investigated. The experimental results revealed that with 0.03% GO addition, the compressive strength of WSAC after curing 1d, 3d, 28d increased by 24.1%, 18.6% and 21.5% compared to control sample, respectively, originating from promoting the hydration process and ettringite crystal growth in WSAC by GO. The heavy metal ion Cr(III)-exchanged by the Al(III) in ettringite crystal follows the Langmuir model with high exchange capacities, qm, 108.46 mg/g for GO-WSAC and 105.73 mg/g for WSAC. The GO-WSAC retains more excellent heavy metal ion removal capacity (95.2 mg/g, initial adsorbent dosage of 0.4 g) in very high concentration (400 mg/L), and the adsorption equilibrium could be reached basically within 10 min. When multiple ions coexist (Zn(II), Cu(II), Cr(III) and Cd(II)), WSAC and GO-WSAC still exhibit excellent removal efficiency, as high as 95.9% and 96.7%, respectively, apart from Cd(II) (only 75.03% and 89.3%, respectively). The findings in our research make WSAC as a new, environmentally friendly and cost-effective adsorbent for heavy metal ions removal from wastewater.

Influence of Cr (VI) concentration on Cr (VI) reduction and electricity production in microbial fuel cell.

Microbial fuel cell is an efficient technology to reduce pollutants of the heavy metal ions. Herein, a dual-chamber microbial fuel cell (MFC) coupled with abio-cathode and electrochemically active bacteria is fabricated to treat Cr (VI) containing wastewater and harvest bioelectricity simultaneously. To investigate the wide application of MFC for various industries, four different concentrations of Cr (VI) (6 mg/L, 15 mg/L, 40 mg/L, 100 mg/L) are used to explore the removal efficiency of Cr (VI) and the corresponding power performance. We find that the power performance gradually increases with the increment of the initial Cr (VI) concentration. Significantly, a maximum power density of 35.3 mW/m2 can be achieved with the initial concentration of 100mg/L Cr (VI), while MFC only generate negligible power density (2.6 mW/m2) without the presence of Cr (VI). Meanwhile, MFC combined with the initial Cr (VI) concentration of 15 mg/L shows the highest Cr (VI) removal of 66.5%. Moreover, partial precipitates are found on the cathode surface and X-ray photoelectron spectroscopy (XPS) analysis has demonstrated that the Cr (VI) is successfully reduced into Cr (III). This study offers an alternative technology to remove Cr (VI) and synchronous electricity generation.

Nanoscale zero-valent iron particles supported on sludge-based biochar for the removal of chromium (VI) from aqueous system.

Biochar (BC) obtained by the co-pyrolysis of municipal sewage sludge (MSS) and sunflower seed shells (SSS) was utilized to support nanoscale zero-valent iron particles (nZVI) for the synthesis of a composite material (nZVI-BC) for Cr(VI) removal from aqueous systems. A series of characterization methods confirmed successful immobilization of nZVI on the surface of biochar with no aggregation. Batch experiments showed that the initial pH, initial Cr(VI) concentration, and nZVI-BC dose all significantly affected the Cr(VI) removal using nZVI-BC. The kinetics for Cr(VI) removal via nZVI-BC could be better explained by the pseudo-second-order (PSO) adsorption model. Adsorption isotherms analysis demonstrated the superior Cr(VI) removal capability of nZVI-BC in comparison to bare nZVI and BC. nZVI-BC can be reused after the regeneration process by applying 0.1 M H2SO4 and 0.1 M NaBH4 solutions. The reaction mechanism for Cr(VI) removal might involve its chemical reduction on the nZVI-BC surface. Overall, environmentally friendly nZVI-BC was highly efficient in Cr(VI) removal from aqueous systems.

Interconnected hierarchical nickel-carbon hybrids assembled by porous nanosheets for Cr(VI) reduction with formic acid

Magnetic carbon materials promise distinct advantages in the decontamination of heavy metal ions. In this work, a novel interconnected hierarchical nickel-carbon (Ni@IHC) hybrid was synthesized by combining the solvothermal method with a one-step pyrolysis under argon atmosphere. Benefitting from 3D flower-like morphology, interconnected porous nanosheets, large surface area, and abundant Ni nanoparticles, Ni@IHC hybrids can remove Cr(VI) within 25 min by using formic acid (FA) as a reductant at 25 ℃. Furthermore, the experimental parameters that can affect the material catalytic performance such as initial Cr(VI) concentration, catalyst dosage, FA concentration, and temperature were also investigated in detail. It was found that highly dispersed Ni nanoparticles contributed significantly to the reduction process. More importantly, the embedded Ni nanoparticles favor fast separation by a magnet and were helpful for the recycles use. This Ni@IHC hybrid was obtained by a facile and easy scale-up method, resulting in the fast transformation of Cr(VI) into Cr(III).

Response surface design for removal of Cr(VI) by hydrogel-supported sulfidated nano zero-valent iron (S-nZVI@H).

In this study, a new sulfidated nanoscale zero-valent iron (S-nZVI) supported on hydrogel (S-nZVI@H) was successfully synthesized for the removal of chromium (Cr) (VI) from groundwater. The surface morphology, dispersion phenomenon and functional groups of novel S-nZVI@H were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Box-Behnken design (BBD) optimization technology based on response surface methodology (RSM) is applied to demonstrate the influence of the interaction of S-nZVI@H dose, initial Cr(VI) concentration, contact time, and initial pH with the Cr(VI) removal efficiency. The analysis of variance results (F = 118.73, P < 0.0001, R2 = 0.9916) show that the quadratic polynomial model is significant enough to reflect the close relationship between the experimental and predicted values. The predicted optimum removal conditions are: S-nZVI@H dose 9.46 g/L, initial Cr(VI) concentration 30 mg/L, contact time 40.7 min, and initial pH 5.27, and the S-nZVI@H dose is the key factor affecting the removal of Cr(VI). The predicted value (99.76%) of Cr (VI) removal efficiency is in good agreement with the experimental value (97.75%), which verifies the validity of the quadratic polynomial model. This demonstrates that RSM with appropriate BBD can be utilized to optimize the design of experiments for removal of Cr(VI).

The role of extracellular polymeric substances (EPS) in the reduction of Cr(VI) by Pannonibacter phragmitetus BB

Cr(VI) contamination is a worldwide environmental problem, and bacterial reduction is considered a promising method for Cr(VI) remediation. In the present study, the role of extracellular polymeric substances (EPS) in the remediation of Cr(VI) by Pannonibacter phragmitetus BB was thoroughly studied. The results showed that the secretion of protein-fraction EPS by P. phragmitetus BB was significantly induced by Cr(VI), which increased from 382.70 to 1483.29 μg/mL with the increase of the initial Cr(VI) concentration (48–60 h). The polysaccharide content in slime EPS (SL-EPS) and loosely bound EPS (LB-EPS) increased gradually with time when the Cr(VI) concentration increased from 0 to 200 mg/L, with the highest polysaccharide content being higher than 2500 μg/mL. In contrast, the change in polysaccharides in tightly bound EPS (TB-EPS) was insignificant (p < 0.05). When the Cr(VI) concentration was higher than 200 mg/L, the secretion of polysaccharide-fraction EPS was inhibited (lower than 1000 μg/mL). Moreover, EPS removal inhibited the growth of P. phragmitetus BB and decreased Cr(VI) reduction efficiency. The adsorption capacity of intact cells to chromium was higher than that of EPS-free cells, which was fit with the Freundlich adsorption model with an R2 value of 0.96. FTIR and XPS analyses demonstrated that intact cells had a higher adsorption capacity for Cr(VI) than EPS-free cells and that Cr(III) mainly existed as Cr2O3, Cr(OH)3, CrCl3 or organic-Cr(III). In addition, the protein-fraction EPS had a critical role in Cr(VI) remediation, and the main functional groups were amine, carboxyl, hydroxyl and phosphate groups.

Nano-Porous-Silicon Powder as an Environmental Friend.

Nano-porous silicon (NPS) powder synthesis is performed by means of a combination of the ultra-sonication technique and the alkali chemical etching process, starting with a commercial silicon powder. Various characterization techniques {X-ray powder diffraction, transmission electron microscopy, Fourier Transform Infrared spectrum, and positron annihilation lifetime spectroscopy} are used for the description of the product’s properties. The NPS product is a new environmentally friendly material used as an adsorbent agent for the acidic azo-dye, Congo red dye. The structural and free volume changes in NPS powder are probed using positron annihilation lifetime (PALS) and positron annihilation Doppler broadening (PADB) techniques. In addition, the mean free volume (VF), as well as fractional free volume (Fv), are also studied via the PALS results. Additionally, the PADB provides a clear relationship between the core and valence electrons changes, and, in addition, the number of defect types present in the synthesized samples. The most effective parameter that affects the dye removal process is the contact time value; the best time for dye removal is 5 min. Additionally, the best value of the CR adsorption capacity by NPS powder is 2665.3 mg/g at 100 mg/L as the initial CR concentration, with an adsorption time of 30 min, without no impact from temperature and pH. So, 5 min is the enough time for the elimination of 82.12% of the 30 mg/L initial concentration of CR. This study expresses the new discovery of a cheap and safe material, in addition to being environmentally friendly, without resorting to any chemical additives or heat treatments.

Microscopic mechanism about the selective adsorption of Cr(VI) from salt solution on nitrogen-doped carbon aerogel microsphere pyrolysis products

A series of nitrogen-doped carbon aerogels (NCAs) were obtained through phase reaction polymerization and different carbonization temperatures to enhance adsorption efficacy of hexavalent chromium (Cr[VI]) from wastewater significantly. Factors that influence adsorption properties of carbon aerogel microspheres toward Cr(VI), such as pH, adsorbent content, initial Cr(VI) concentrations, and coexisting anion, were investigated. Three isotherm (Langmuir, Freundlich, and Sips) and three kinetic (pseudofirst-order, pseudosecond-order, and Elovich) models were used to interpret the adsorption process. The adsorption capacity of Cr(VI) reached 180.62 mg·g−1, which was superior to that of most aerogel adsorbents. In addition to the adsorption effect, the XPS results also showed that N-containing groups on the NCA surface reduce the adsorbed Cr(VI) to the less toxic Cr(III). The prepared sorbent demonstrates a negligible loss in adsorption capacity after 6 cycles. NCAs show acceptable application prospects in selective removal of Cr(VI) ions.

Reduction-adsorption of chromium(VI) by using IL-imprinted resin -innovative solution for water purification

Novel sorbents (poly(vinylbenzyl chloride-co-divinylbenzene) functionalized with Ionic Liquids precursors- hydrophobic and hydrophilic 3- and 4-pyridineketone and oxime were prepared for application to chromium removal. The fabricated materials were extensively characterized (surface morphology, FT-IR, NMR, Raman, microscopy, XPS, and wettability). The efficiency of functionalization of poly(vinylbenzyl chloride-co-divinylbenzene was demonstrated not only in the process of adsorption of chromium(VI), but also in its reduction to a less toxic form of trivalent ions. I was shown that the efficiencies of both processes depended on the time, pH of the aqueous phase and the initial concentration of Cr(VI). At pH of 0 the cumulative chromium removal was preferable (removal almost 1200 mg of Cr) with the reduction as the dominant process. At pH of 3.5 and higher only adsorption was observed with the maximum capacity of 144.4 mg/g. The conducted analytical techniques, such as Raman and XPS, enabled to determine the mechanism of the sorption and the surface Cr(VI) reduction that oxidize water to O2. The studies indicated that this research direction was forward-looking and fits in with the trends of a sustainable development- simultaneous reduction and adsorption of chromium from wastewater.

The reuse of disposable COVID-19 surgical masks as a nitrogen-enrichment agent and structure promotor for a wild plant-derived sorbent

In this work, disposable surgical face masks (SFMs) have been utilized as nitrogen (N)-doping agents for carbon (C) adsorbents through thermal carbonization using K2CO3 as activators. A readily available wild-plant biomass (Cyperus papyrus, CP) was chosen as the raw material for manufacturing the adsorbent. A “green-etching” process was employed to synthesize adsorbents with significant modifications and without using of any chemicals. As observed via characterization analysis, upon mixing SFMs with CP at a 1:1 weight ratio, there were considerable developments in the specific surface area (SBET = 830 m2/g) for both micro- (0.333 cm3/g) and mesopores (0.053 cm3/g) as well as diversified functional groups (e.g., amino and carbonyl) on the sorbent that was produced. This is a key for the adsorbent’s ability in order to remove a variety of pollutants from aqueous solutions. The heavy metal (Cr(VI)) ion adsorption capacity was used to identify the optimum adsorption parameters. Significantly lower amounts of Cr(VI) residues were achieved at a concentration of 2 mg/L from an initial Cr(VI) concentration of 30 mg/L by applying an SFM-modified sorbent dose of 10 g/L. The outcomes of this research could be advantageous for decision making in plastic waste management that surged during the COVID-19 pandemic.