Removal of Cu(II) and Cr(VI) from wastewater by an amphoteric sorbent based on cellulose-rich biomass

Luminescent carbon dots-rooted polysaccharide crosslinked hydrogel adsorbent for sensitive determination and efficient removal of Cu2

In this study, a novel luminescent carbon dot-rooted polysaccharide hydrogel (CDs@CCP hydrogel) was prepared by crosslinking cellulose, chitosan (CS), and polyvinyl alcohol (PVA) for simultaneous fluorescent sensing and adsorption of Cu2+. The crosslinking of these low-cost, polysaccharide polymers greatly enhance the mechanical strength of the composite hydrogel while making the polysaccharide-based adsorbent easy to reuse. This composite hydrogel exhibited an excellent adsorption capacity (124.7 mg∙g-1) for residual Cu2+ in water, as well as a sensitive and selective fluorescence response towards Cu2+ with a good linear relationship (R2 > 0.97) and a low detection limit (LOD) of 0.02 μM. The adsorption isotherms, adsorption kinetics, and thermodynamics studies were also conducted to investigate the adsorption mechanism. This composite hydrogel offers an efficient tool for simultaneous monitoring and treatment of Cu2+ from wastewater.

Enhanced synergistic removal of Cu(II) and Cr(VI) with multifunctional biomass hydrogel from strong-acid media

Simultaneous recovery of heavy metal ions (HMIs) such as Cu(II) and Cr(VI) from strong-acid media was a great challenge due to the inhibition of protons. Herein, a novel biomass hydrogel (CMC/PEI-PD) containing various groups (bis-picolylamine, amino, and hydroxyl groups) was newly prepared by a facile two-step process. The static experiments relating pH, kinetics and isothermal co-adsorption confirmed the synergistic effect towards Cu(II) and Cr(VI) consistently. Specifically, the adsorption capacities of Cu(II) and Cr(VI) at pH 2.0 increased by 23.73% and 40.18% in comparison with the single systems. Moreover, coexistence of inorganic anions and cations could further increase the adsorption of Cu(II) and Cr(VI) by 59.90% and 43.39%, respectively. At the same time, the adsorption and desorption ratios for both HMIs remained stable. The superior performance came from the two dominant mechanisms of co-removal. On the one hand, Cu(II) chelated by bis-picolylamine group attracted Cr(VI) in the form of cation bridge, thus promoting Cr(VI) adsorption. On the other hand, the protonated amine group attracted Cr(VI) by electrostatic interaction and weakened the inter-cationic repulsion by electrostatic shielding, thus promoting Cu(II) adsorption. In addition, the dynamic column experiment towards simulated acidic electroplating wastewater involving Cu(II)-Cr(VI)-Ni(II) certified the high efficiency and feasibility of the co-removal. Therefore, CMC/PEI-PD owned great potential in the separation of typical HMIs even directly from strong-acid media.

Design of amphoteric MOFs-cellulose based composite for wastewater remediation: Adsorption and catalysis

Water pollution remains a serious problem for aquatic organism and human beings. Developing an efficient material which can simultaneously remove and convert pollutants into low or no harmful compounds is an essential issue. Targeting at this goal, a multifunctional and amphoteric wastewater treatment material of Co-MOF and functionalized cellulose-based composite (CMC/SA/PEI/ZIF-67) was designed and prepared. Carboxymethyl cellulose (CMC) and sodium alginate (SA) were selected as support to construct an interpenetrating network structure and made it crosslinked with polyethyleneimine (PEI) for further in situ growth of ZIF-67 with good dispersion. The material was characterized using an appropriate set of spectroscopic and analytical techniques. When applied in the adsorption of heavy metal oxyanions with no adjustment of pH, the adsorbent could completely decontaminate Cr(VI) at both low and high initial concentrations with good reduction rates. The adsorbent maintained good reusability after five cycles. Meanwhile, the cobalt species of CMC/SA/PEI/ZIF-67 can activate peroxymonosulfate to generate high oxidizing substances (such as SO4-· and ·OH- radicals) to degrade cationic rhodamine B dye within 120 min, thus indicating the amphoteric and catalytic nature of our CMC/SA/PEI/ZIF-67 adsorbent. The mechanism of the adsorption and catalytic process was also discussed based with the assistance of different characterization analysis.

A Comparative Study of Mechanism and Performance of Anionic and Cationic Dialdehyde Nanocelluloses for Dye Adsorption and Separation

In this study, anionic dialdehyde cellulose (DAC) and cationic dialdehyde cellulose (c-DAC) nanofibrous adsorbents were prepared via a two-step reaction from bamboo pulp, using sodium periodate and Girard's reagent T as oxidizing and cationizing agents, respectively. The performance of DAC and c-DAC for selective dye adsorption and separation was evaluated by six different organic dyes (with varying charge properties) and certain binary mixtures. Both adsorbents could remove the dyes but with different capability, where DAC exhibited high adsorption efficiency against cationic dyes (e.g., the maximum adsorption capacity for Bismarck brown Y was 552.1 mg/g) and c-DAC exhibited high adsorption efficiency against anionic dyes (e.g., the maximum adsorption capacity for Congo red was 540.3 mg/g). To investigate the adsorption mechanism for these adsorbents, effects of contact time, initial pH value, initial dye concentration, and ionic strength on the adsorption activity against Congo red were investigated. The adsorption equilibrium data of DAC were found to fit best with the Langmuir isotherm model, whereas that of c-DAC were found to fit best with the Freundlich model. Both DAC and c-DAC adsorption kinetic data could be described by the pseudo-second-order kinetic model, and these adsorbents possessed stable adsorption efficiency in the pH range of 4-10. Furthermore, their dye adsorption capabilities were found to increase with increasing ionic strength (salt concentration). The distinctive complementary features of DAC and c-DAC will allow them to remove a wide range of organic dyes from industrial wastewater.

Regulation of hydrogen bonding network between cellulose nanofibers by rare earth ion Y3

Cellulose is regarded as the most abundant biomass, and nanocellulose derived from it has numerous applications in environmentally friendly materials. However, owing to the abundant hydroxyl groups on surface, nanocellulose is prone to agglomeration when transported, stored, or made into materials, which destroys material performance and limits its use. In this study, a feasible method was presented for regulating the hydrogen bonding strength between cellulose nanofibers (CNFs) by adding a minute quantity of rare earth ions Y³⁺ during cellulose nanofibrillation. It was found that the strength of hydrogen bonding between CNFs can be regulated by controlling the quantity of Y³⁺ in the system. The dispersibility and stability of CNFs, as well as the mechanical properties of CNFs films and CNFs-reinforced papers can be improved by 43.07 % and by 64.05 % after adding only 0.05 or 0.075 wt% Y³⁺. The possible mechanism of CNFs hydrogen bonding network reconstruction was proposed.

Hydroxyapatite@Mn-Fe composite as a reusable sorbent for removal of Nile blue dye and Cr(VI) from polluted water

In this study, hydroxyapatite@Mn-Fe composite was used as a novel adsorbent to eliminate Nile blue (NB) dye and hexavalent chromium ion (Cr(VI)) from aqueous media. Different analyses such as FTIR, Map, SEM, EDX, BET, and XRD were used to study the characteristics of the composite. The highest sorption efficiencies of Cr(VI) and NB at pH 2 and 10 were 97.63% and 98.83%, respectively, which are significant values. Equilibrium and kinetic studies of the sorption process showed that the Freundlich isotherm model and pseudo-second-order kinetic model can better describe the equilibrium and kinetic behavior of the sorption process. According to the Langmuir model, the maximum sorption capacities of NB dye and Cr(VI) ion using the hydroxyapatite@Mn-Fe composite were 0.259 and 0.938 mmol/g, respectively. Also, the results of the thermodynamic study showed that the sorption process is favorable (ΔS° =  - 34.2 kJ/mol·K for Cr(VI) and - 144.6 kJ/mol·K for NB), spontaneous (ΔG° < 0), and exothermic (ΔH° =  - 27.99 kJ/mol for Cr(VI) and - 64.2 kJ/mol for NB). Moreover, the desorption process of both contaminants using the hydroxyapatite@Mn-Fe composite showed that the H₂SO₄ solution with a concentration of 3 mol/L can remove both contaminants separately with the highest efficiency. Furthermore, the reusability study indicated that the composite can be used in five reuse cycles without significant decrease in its efficiency. Besides, the composite was able to eliminate color, turbidity, COD, and BOD₅ from the textile wastewater with removal efficiencies of 93.06, 81.61, 76.05, and 71.88%, respectively. To the best of our knowledge, hydroxyapatite@Mn-Fe composite was synthesized and used for the first time to remove Cr(VI) ions and NB dye. In general, the aforementioned composite is recommended for industrial wastewater treatment.

Novel diaminoguanidine functionalized cellulose: synthesis, characterization, adsorption characteristics and application for ICP-AES determination of copper(II), mercury(II), lead(II) and cadmium(II) from aqueous solutions

In this study, the novel adsorbent diaminoguanidine-modified cellulose (DiGu.MC) was synthesized to extract mercury, copper, lead and cadmium ions from aqueous solutions and environmental water samples. The synthetic strategy involved oxidizing cellulose powder into dialdehyde cellulose (DAC) and reacting DAC with diaminoguanidine to create an imine linkage between the two reactants to form diaminoguanidine-modified cellulose (DiGu.MC). The structure and morphology of the adsorbent were studied using a variety of analytical techniques including Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) surface area measurements. Adsorption of mercury, copper, lead, and cadmium ions was optimized by examining the effects of pH, initial concentration, contact time, dose, temperature and competing ions. Under optimal adsorption conditions, the adsorption capacities of Cu²⁺, Hg²⁺, Pb²⁺, and Cd²⁺ were 66, 55, 70 and 41 mg g⁻¹, respectively. The adsorption isotherm is in very good agreement with the Langmuir isotherm model, indicating that a monomolecular layer is formed on the surface of DiGu.MC. The kinetics of adsorption are in good agreement with the pseudo-second kinetics model that proposes the chemical adsorption of metal ions via the nitrogen functional groups of the adsorbent. Thermodynamic studies have confirmed that the adsorption of heavy metals by DiGu.MC is exothermic and spontaneous. Regeneration studies have shown that the adsorbent can be recycled multiple times by removing metal ions with 0.2 M nitric acid. The removal efficiency for regeneration was over 99%. DiGu.MC is introduced as a unique adsorbent in removing mercury, copper, lead and cadmium with a simple synthetic strategy, with cheap starting materials, a unique chemical structure and fast adsorption kinetics leading to excellent removal efficiency and excellent regeneration. The mechanism of adsorption of the investigated heavy metals, is probably based on the chelation between the metal ions and the N donors of DiCu.MC.

A facile modification of cation exchange resin by nano-sized goethite for enhanced Cr(VI) removal from water

A novel macroporous strong acidic cation exchange resin (D001) modified by nano-sized goethite (nFeOOH@D001) was fabricated by using a facile ethanol dispersion and impregnation method, and its efficiency for Cr(VI) removal was tested thereafter. Due to the dispersing effect of ethanol, FeOOH particles of 20-150 nm were coated on the D001 surfaces. The nFeOOH@D001 obtained a Cr(VI) removal efficiency and capacity of 80.2% and 7.4 mg/g respectively, 5 times and 8 times higher than that of the pristine D001. The Cr(VI) removal by nFeOOH@D001 followed the pseudo second-order kinetics and the Langmuir adsorption model. Column experiments also demonstrated that the nFeOOH@D001 exhibited a much better ability to remove Cr(VI) as compared to the D001. Additionally, the nFeOOH@D001 showed a potential for reusability and renewability. The adsorbed nFeOOH@D001 could be easily desorbed by 0.1 M acetic acid and a reuse efficiency of 92.7% could be maintained after 4 desorption-adsorption cycles. The used nFeOOH@D001 could be eluted by 0.1 M HCl to remove nFeOOH, and the renewed D001 could be recoated by nFeOOH and achieved a regeneration rate of 97.8% for Cr(VI) removal. The above results indicated that nano-sized goethite modification is a promising method to endow D001 with the ability to remove Cr(VI) from water.

A one step synthesis of hybrid Fe/Ni-rGO using green tea extract for the removal of mixed contaminants

The use of biomass for the synthesis of value-added products, such as functional nanomaterial for the removal of contaminants, is a challenge. In this study, hybrid bimetallic Fe/Ni nanoparticles and reduced graphene supported bimetallic Fe/Ni nanoparticles (Fe/Ni-rGO) were prepared via a one-step green synthesis using green tea extract, and thereafter evaluated for the simultaneous removal of rifampicin (RIF) and Pb(II) from aqueous solution. The efficiencies of Pb(II) and RIF removal by Fe/Ni-rGO were 87.5 and 96.8%, respectively. The removal performance of the hybrid Fe/Ni-rGO was better than either nFe/Ni, rGO, or Fe-rGO. Detailed characterization and analyses of Fe/Ni-rGO indicated that both Fe and Ni nanoparticles were evenly distributed over the surface of rGO and that aggregation of Fe, Ni nanoparticles, and stacking of rGO in the hybrid were decreased. Furthermore, while LC-TOF-MS analysis showed that RIF was degraded into small-molecule fragments, XPS showed that Pb(II) was not reduced to Pb⁰. The major conditions impacting removal efficiency, adsorption kinetics, and fit to adsorption isotherm models were examined to better understand the removal mechanism. While the adsorption of both contaminants fit well a pseudo-second-order kinetic model, the adsorption of RIF fit the Freundlich isotherm model best, while the adsorption of Pb(II) fit the Langmuir isotherm model best. Thus, the removal mechanism of both contaminants firstly being chemical adsorbed onto the surface, while nFe/Ni continues to participate in the catalytic reduction of RIF. Moreover, Fe/Ni-rGO could be reused and performed well for wastewater treatment, thus suitable as a practical resource recycling technology.

Synthesis of wheat bran sawdust/Fe3O4 composite for the removal of methylene blue and methyl violet

Magnetically modified nanomaterials have recently gained a great attention in wastewater treatment. In this study, the uptake process of methylene blue (MB) and methyl violet (MV) from aqueous media using wheat bran sawdust/Fe₃O₄ composite was studied. To specify the surface and structural properties of the wheat bran sawdust/Fe₃O₄ composite, various analyses such as FTIR, XRD, EDX, Map, TGA/DTG, SEM, VSM, and BET were performed. The results of BET analysis indicated that the specific surface area of the aforementioned composite was 74.25 m²/g, and the average pore size was 65.7A, which indicates that the composite has a mesoporous structure. Also, VSM analysis indicated that the composite has a paramagnetic property with a magnetic saturation of 28.29 emu/g and can be easily eliminated from the aqueous solution by a magnet. Moreover, the highest removal efficiency of MB and MV dyes using the wheat bran/Fe₃O₄ composite was obtained as 97.46 and 98.75%, respectively, which were significant values. These removal efficiencies were obtained at contact time of 50 min and pH values of 9 and 8 for MB and MV, respectively. Furthermore, the outcomes of equilibrium study showed that the Langmuir model with a correlation coefficient greater than 0.98 describes the equilibrium behavior of the uptake process better than the Freundlich and Dubinin-Radushkevich models. Besides, the maximum sorption capacity of MV and MB dyes using the Langmuir model was obtained as 46.08 and 51.28 mg/g, respectively. Also, the uptake process followed the pseudo-second-order kinetic model, and the thermodynamic study indicated that the uptake process is exothermic and spontaneous.

Enhanced adsorption of copper ions by phosphoric acid-modified Paeonia ostii seed coats

Novel adsorbent, phosphoric acid-modified Paeonia ostii seed coats (PA-PSC) were successfully prepared by low-temperature pyrolysis to effectively remove Cu(II) from aqueous solution. The results revealed that equilibrium adsorption capacity (q_e) of PA-PSC for Cu(II) was notably enhanced up to 4-folds compared with the raw PSC. FT-IR and XPS analyses suggested that the adsorption of Cu(II) by PA-PSC was primarily ascribed to electrostatic forces and complexing effects. Besides, equilibrium and kinetic studies demonstrated that Freundlich and pseudo-second-order models were the actually fairly good approximations of Cu(II) adsorption. Thermodynamic analysis revealed that the adsorption of Cu(II) onto PA-PSC was a chemical, endothermic, and spontaneous process. Lastly, reusability study further confirmed the applicability of PA-PSC as a promising adsorbent for removing Cu(II) from aqueous solution.

Adsorption of copper ions from solution using xanthate wheat straw

To enhance adsorption capacity of wheat straw (WS) toward copper ion from solution, carbon disulfide was used to modify WS by a facile grafting method through epichlorohydrin and ethylenediamine. So WS containing xanthate groups (XWS) was obtained. The XWS was characterized using elemental analysis, X-ray diffraction, infrared spectroscopy and adsorption property of XWS toward copper ions. The results showed that S was introduced into the surface of WS. The solution pH was in favor of Cu²⁺ adsorption at pH 5, while NaCl existing in solution was slightly favorable for adsorption. The adsorption kinetic followed the pseudo-second-order kinetic model, while the adsorption isotherm curve was well fitted using the Langmuir model. The adsorption capacity was 57.5 mg·g^-1 from experiment. The process was entropy-produced, endothermic and spontaneous in nature. The column adsorption was performed and Yan model was good to predict the breakthrough curve. XWS as adsorbent is promising to remove copper ions from solution, and this offers one way of effective utilization of waste byproduct from agriculture.

A systematic review on carbohydrate biopolymers for adsorptive remediation of copper ions from aqueous environments-part A: Classification and modification strategies

Copper is one of the most toxic heavy metals which must be eliminated from aqueous environments, according to the environmental standards. Carbohydrate biopolymers are promising candidates for synthesizing copper-adsorbent composites. It is due to unique properties such as having potential adsorptive functional sites, availability, biocompatibility and biodegradability, formability, blending capacity, and reusability. Different types of copper-adsorbent carbohydrate biopolymers like chitosan and cellulose with particular focus on the synthesizing and modification approaches have been tackled in this review. Composites, functionality and morphological aspects of the biopolymer adsorbents have also been surveyed. Further progress in the fabrication and application of biopolymer adsorbents would be achievable with special attention to some critical challenges such as the process economy, copolymer and/or (nano) additive selection, and the physicochemical stability of the biopolymer composites in aqueous media.

Surface modification of biomaterials based on cocoa shell with improved nitrate and Cr(vi) removal

The present work addresses the development of simple, low-cost and eco-friendly cocoa-shell-based materials for efficient removal of heavy metal hexavalent chromium (Cr(vi)), and toxic nitrate (NO3 -) from aqueous solution. A conventional treatment process was used to purify cocoa shell (CS) into an adsorbent, followed by chemical grafting of dendrimers to promote its surface properties for nitrate and Cr(vi) removal. The morphology, surface charge, structure and stability of the new adsorbent were investigated by scanning electron microscopy, Fourier transform infrared and UV-visible spectroscopies, zeta potential, X-ray photoelectron spectrometry, and differential scanning calorimetry. The successful chemical grafting of the dendrimer (polyethyleneimine, PEI) onto purified CS was confirmed. CS-T-PEI-P proved to be a very efficient candidate for the removal of nitrate and chromium(vi). Removal of the two pollutants at different initial concentrations and pH values was studied and discussed. Sorption of chromium and nitrate was found to obey 2nd-order kinetics and a Freundlich-type isotherm, affording an uptake adsorption of 16.92 mg g-1 for NO3 - and 24.78 mg g-1 for Cr(vi). These results open promising prospects for its potential applications as a low cost catalyst in wastewater treatment.

Simultaneous removal of mixed contaminants triclosan and copper by green synthesized bimetallic iron/nickel nanoparticles

The mixed contamination of environmental matrices by antibacterial agents and heavy metals has attracted much attention worldwide due to the complex nature of their environmental interactions and their potential toxicity. In this work, green synthesized bimetallic iron/nickel nanoparticles (Fe/Ni NPs) was used to simultaneously remove triclosan (TCS) and copper (Cu (II)) under optimal experimental conditions with removal efficiencies of 75.8 and 44.1% respectively. However, in a mixed contaminant system the removal efficiencies of TCS and Cu (II) were lower than when TCS (85.8%) and Cu (II) (52.5%) were removed separately, suggesting that there was competitive relationship between the two contaminants and Fe/Ni NPs used for remediation. SEM-EDS, XRD and FTIR all indicated that both TCS and Cu (II) were adsorbed onto Fe/Ni NPs. Furthermore, while XPS showed that Cu (II) was reduced to Cu⁰, GC-MS analysis showed that TCS also underwent degradation with 2,7/2,8-Cl₂DD as the major intermediate. The adsorption of both contaminants fit well a pseudo second order kinetic model (R²>0.998) and the Freundlich isotherm (R²>0.905). Whereas the reduction kinetics obeyed a pseudo first order model. Thus, overall the removal of TCS and Cu (II) involved a combination of both adsorption and reduction. Finally, a removal mechanism for triclosan and Cu (II) was proposed. Overall, Fe/Ni NPs have the potential to practically coinstantaneously remove both TCS and Cu (II) from aqueous solution under a wide range of conditions.

Highly effective removal of Cu(II) in aqueous solution by using mesoporous TiO2

Mesoporous TiO₂ has been prepared by a brief and simple sol-gel processing and applied for the removal of Cu(II) from aqueous solution. The adsorption behavior of mesoporous TiO₂ for Cu(II) was investigated using batch experiments. Results showed that the pseudo-second-order model and Langmuir isotherm were more accurate to describe the kinetics process and adsorption isotherm. Mesoporous TiO₂ adsorbent displayed excellent Cu(II) adsorption efficiency (195.52mg g^-1). The thermodynamic parameters showed that the adsorption was spontaneous and endothermic. It was also found that mesoporous TiO₂ could be used at least seven times without obvious loss of its original adsorption efficiency. Therefore, the obtained mesoporous TiO₂ could be employed as an effective and low-cost adsorbent for removal of Cu(II) from contaminated effluents.

Elimination performance of methylene blue, methyl violet, and Nile blue from aqueous media using AC/CoFe2O4 as a recyclable magnetic composite

The present paper describes the sono-assisted adsorption (sono-adsorption) of methylene blue (MB), methyl violet (MV), and Nile blue (NB) from aqueous solution by AC/CoFe₂O₄ magnetic composite. FT-IR, TGA-DTG, VSM, XRD, TEM, SEM, EDX, Map, and Raman analysis were used to characterize the magnetic composite. The magnetization saturation value of AC/CoFe₂O₄ magnetic composite was determined to be 53.06 emu/g. Dye sono-adsorption efficiency was increased by increasing adsorbent dose, pH value, and contact time, but not dye concentration. Pseudo-first-order, pseudo-second-order, and intra-particle diffusion models were used to study the kinetic behavior of the cationic dye sono-adsorption. The sono-adsorption kinetics was reasonably followed by pseudo-second-order model (R² > 0.998). The results showed that the Freundlich model (R² > 0.976) was more able to describe the sono-adsorption equilibrium behavior than Langmuir, D-R, and Scatchard models. The maximum sono-adsorption capacity of NB, MV, and MB was determined as 86.24, 83.90, and 87.48 mg/g, respectively. Based on the parameters derived from isotherm modeling (R_L, n, and E), the sono-adsorption process of cationic dyes is desirable and physical. An increase in NaCl concentration reduced the sono-adsorption efficiency for all dyes. Also, the adsorption-desorption of AC/CoFe₂O₄ magnetic was studied up to 10 stages, and it was confirmed that the sono-adsorption efficiency is acceptable up to the eight stage. AC/CoFe₂O₄ magnetic composite is, therefore, an affordable and recyclable adsorbent to remove the molecule of NB, MV, and MB dyes from aqueous media.

Cr(VI) reduction by an extracellular polymeric substance (EPS) produced from a strain of Pseudochrobactrum saccharolyticum

A better understanding of the Cr(VI) reduction position and mechanisms by a Cr(VI)-reducing strain is important for the bioremediation of Cr pollution in the environment. In the present study, we were interested in figuring out the role of extracellular polymeric substances (EPS) as the main area for Cr(VI) reduction in the newly reported strain of Pseudochrobactrum saccharolyticum LY10. We investigated the subcellular distribution and reduction capability of each cellular component as the main area of Cr(VI) reduction by scanning electron microscopy and soft X-ray spectromicroscopy. The results suggested that most of Cr was presented in the supernatants as Cr(III) after reduction. In the cells, Cr was mostly distributed in the EPS and cell wall, while the EPS had the maximum Cr(VI) reduction rate (81.5%) as compared with the cell wall (30.1%). Soft X-ray spectromicroscopy analysis indicated that Cr accumulated more in the EPS. Therefore, the results suggested that the EPS were the main area for Cr(VI) reduction in the bacteria of P. saccharolyticum LY10.

Effect of pH on hexavalent and total chromium removal from aqueous solutions by avocado shell using batch and continuous systems

Solution pH appears to be the most important regulator of the biosorptive removal of chromium ions from aqueous solutions. This work presents a kinetic study of the effects of solution pH on Cr(VI) and total chromium removal from aqueous solution by Hass avocado shell (HAS) in batch and continuous packed bed column systems. Different Cr(VI) and total chromium removal performances of HAS were obtained in pH-shift batch, pH-controlled batch, and continuous systems. These results emphasize the great importance of determining the most appropriate pH for Cr(VI) and total chromium removal, considering the operational mode of the proposed large-scale treatment system. Total chromium biosorption batch kinetics was well described by the Elovich model, whereas in the continuous system, the fitness of the kinetic models to the experimental data was pH dependent. X-ray photoelectron spectroscopy and kinetic studies clearly indicated that the reaction mechanism of Cr(VI) with HAS was the reductive biotransformation of Cr(VI) to Cr(III), which was partially released to the aqueous solution and partially biosorbed onto HAS.

Biosorptive application of defatted Laurus nobilis leaves as a waste material for treatment of water contaminated with heavy metal

Defatted Laurus nobilis leaves as a natural biosorbent was first evaluated for elimination of toxic heavy metals such as Pb(II), Cd(II), Zn(II), Cu(II) from aqueous solutions for its wide availability as forest industry waste, in this study. The effects of solution pH, contact time, biosorbent dosage, initial metal ions concentration, ionic strength, humic acid effect, and their competitive effect on the biosorption of lead(II), cadmium(II), Copper(II), and zinc(II) by defatted Laurus nobilis leaves waste (LW) were studied for each metal. The biosorbent was characterized using FT-IR and SEM images. Comparative isotherm and kinetic studies were performed. The sorption of Cd(II) and Zn(II) on LW fitted better in the Freundlich model but Pb(II) and Cu(II) sorption fitted better in the Langmuir model. From the obtained results, the pseudo-second-order kinetic model described the biosorption of cadmium, lead, zinc copper ions the best. The biosorbent showed the maximum biosorption capacities (q_m) of 96.2, 8.6, 8.7, and 6.0 mg g^-1 for lead, cadmium, zinc, and copper, respectively. These results indicated that LW may be used as an effective and inexpensive heavy metal remediation material. Comparison to previous studies showed that LW is also comparable to (or better than) several other biosorbents.

Research on adsorption of Cr(Ⅵ) by Poly-epichlorohydrin-dimethylamine (EPIDMA) modified weakly basic anion exchange resin D301

A novel composite, EPIDMA/D301, with high adsorption capacity and particular affinity toward Cr(Ⅵ) was well prepared utilizing cationic polyelectrolyte poly-epichlorohydrin-dimethylamine (EPIDMA) impregnated in the networking pores of the styrene macroporous weak basic anion exchange resin D301. The physicochemical characteristics of EPIDMA/D301 were characterized by the Brunauer-Emmett-Teller (BET), zeta potential, FTIR, SEM-Mapping and XPS. The adsorption properties were researched via the influence of the concentration of EPIDMA, adsorbent dose, pH, the initial concentration of Cr(Ⅵ) solution, contact time and temperature. Results presented that the weakly basic anion exchange resin supported cationic polymer showed the excellent potential of removing Cr(VI) ions primarily due to the nonspecific Cr(VI) adsorption resulted from the polymeric host D301, the electrostatic attraction of amino groups fixed on the D301 matrix and the embedded EPIDMA with Cr(VI) ions and the ion exchange by the displacement of Cl^- mainly derived from EPIDMA with Cr(VI) ions. The kinetic data were best fitted by the pseudo-second-order kinetic model. The batch equilibrium data followed Langmuir isotherm model well with the maximum adsorption capacity of 194 mg g^-1 at 25 °C, which demonstrated that the styrene anion exchange resin modified with EPIDMA might be an efficient approach to eliminate potentially toxic metals.

Bagasse Cellulose Grafted with an Amino-Terminated Hyperbranched Polymer for the Removal of Cr(VI) from Aqueous Solution

A novel bio-adsorbent was fabricated via grafting an amino-terminated hyperbranched polymer (HBP-NH₂) onto bagasse cellulose. The morphology and microstructure of the HBP-NH₂-grafted bagasse cellulose (HBP-g-BC) were characterized and its adsorption capacity for Cr(VI) ions in aqueous solutions was investigated. The rough surface structure of HBP-g-BC that is beneficial for improving the adsorption capacity was observed by scanning electron microscopy (SEM). The grafting reaction was confirmed by Fourier-transform infrared (FT-IR) spectroscopy. The adsorbent performance was shown to be better with a lower pH value, a higher adsorbent dosage, or a higher initial Cr(VI) concentration. Moreover, the kinetics study revealed that the adsorption behavior followed a pseudo-second-order model. The isotherm results showed that the adsorption data could be well-fitted by the Langmuir, Freundlich, or Temkin models. Moreover, HBP-g-BC could maintain 74.4% of the initial removal rate even after five cycles of regeneration. Thus, the high potential of HBP-g-BC as a bio-adsorbent for heavy metal removal has been demonstrated.

Treatment of model and galvanic waste solutions of copper(II) ions using a lignin/inorganic oxide hybrid as an effective sorbent

A study was made concerning the removal of copper(II) ions from model and galvanic waste solutions using a new sorption material consisting of lignin in combination with an inorganic oxide system. Specific physicochemical properties of the material resulted from combining the activity of the functional groups present in the structure of lignin with the high surface area of the synthesized oxide system (585m²/g). Analysis of the porous structure parameters, particle size and morphology, elemental composition and characteristic functional groups confirmed the effective synthesis of the new type of sorbent. A key element of the study was a series of tests of adsorption of copper(II) ions from model solutions. It was determined how the efficiency of the adsorption process was affected by the process time, mass of sorbent, concentration of adsorbate, pH and temperature. Potential regeneration of adsorbent, which provides the possibility of its reusing and recovering the adsorbed copper, was also analyzed. The sorption capacity of the material was measured (83.98mg/g), and the entire process was described using appropriate kinetic models. The results were applied to the design of a further series of adsorption tests, carried out on solutions of real sewage from a galvanizing plant.

A novel adsorbent TEMPO-mediated oxidized cellulose nanofibrils modified with PEI: Preparation, characterization, and application for Cu(II) removal

This study describes the preparation of a novel adsorbent based on cellulose nanofibrils by first TEMPO mediated oxidation and then PEI grafting (TOCN-PEI) for heavy metal removal. FTIR results demonstrated the successful introduction of the adsorption functional groups (carboxyl and amino groups), and the elemental analysis and acid base titration were used to quantify the contents of these introduced groups. The kinetics curve suited the pseudo-second-order model better and the equilibrium data well fitted the Langmuir model, with the maximum Cu(II) uptake of 52.32mgg(-1). Kinetic study showed that the PEI grafting increased the initial adsorption rate of the TOCN-PEI compared with the adsorbents without PEI. Thermodynamic study was carried out through isothermal titration calorimetry (ITC) measurement and the binding reaction was found to be exothermic and driven by enthalpy change. The adsorption process by TOCN-PEI was pH dependent, and decreasing pH would lead to desorption of Cu(II) ions, thus make the reuse of the absorbent more convenient through adsorption-desorption cycles.

Water soluble EDTA-linked chitosan as a zwitterionic flocculant for pH sensitive removal of Cu(ii) ion

Water soluble EDTA-linked chitosan was synthesized and applied to remove Cu(ii) utilizing its property of chelation and pH sensitive precipitation.

A green technology for the synthesis of cellulose succinate for efficient adsorption of Cd(ii) and Pb(ii) ions

Cellulose succinate, directly prepared by a simple and green mechanical activation-assisted solid-phase synthesis method in a stirring ball mill, was used as environmental-friendly adsorbent for efficient adsorption of heavy metals.

Cost effective nanofiber composite membranes for Cr(vi) adsorption with high durability

PANI/EVOH composite nanofiber membranes were prepared though melt-blending extrusion, high-speed flow deposition and in situ chemical oxidative polymerization for the removal of hexavalent chromium [Cr(vi)].