Equilibrium and molecular mechanism of anionic dyes adsorption onto copper(II) complex of dithiocarbamate-modified starch

Efficient Removal of Congo Red, Methylene Blue and Pb(II) by Hydrochar-MgAlLDH Nanocomposite: Synthesis, Performance and Mechanism

Organic dyes and heavy metals often coexist in industrial effluents, and their simultaneous removal is a grand challenge. Herein, a hydrochar and MgAl layered double hydroxide (HC-MgAlLDH) nanocomposite was prepared via a facile one-step hydrothermal route, and applied to remove anionic Congo red (CR), cationic Methylene blue (MB) and Pb(II) from aqueous solutions. The nanocomposite was formed by interweaving amorphous HC and crystalline MgAlLDH nanoplates and possessed more functional groups, lower zeta potential and larger specific surface area than uncomposited MgAlLDH. Batch removal experiments showed that the components HC and LDH dominated the CR and MB removals, respectively, whereas Pb(II) removal was conjointly controlled by the two components. The maximum Langmuir removal capacities of the nanocomposite to sole CR, MB, or Pb(II) were 348.78, 256.54 or 33.55 mg/g. In binary and ternary systems, the removal capacities of CR and MB only slightly decreased, while the capacity of Pb(II) increased by 41.13-88.61%. The increase was related to the coordination of Pb(II) with the sulfur-containing groups in dyes and the precipitation of PbSO₄. Therefore, the simultaneous removal of CR, MB and Pb(II) was involved in a synergistic effect, including electrostatic adsorption, π-π interaction, coordination and precipitation. The present work shows that the HC-MgAlLDH nanocomposite has great potential for wastewater integrative treatment.

Nitrogen Self-Doping Carbon Derived from Functionalized Poly(Vinylidene Fluoride) (PVDF) for Supercapacitor and Adsorption Application

A new synthetic strategy has been developed for the facile fabrication of a N-doped porous carbon (NC-800) material via a facile carbonization of functionalized poly(vinylidene fluoride) (PVDF). The prepared NC-800 exhibits good specific capacitance of 205 F/g at 1 A/g and cycle stability (95.2% retention after 5000 cycles at 1 A/g). The adsorption capacity of NC-800 on methylene blue and methyl orange was 780 mg/g and 800 mg/g, respectively. The facile and economical method and good performance (supercapacitor and adsorption) suggest that the NC-800 is a promising material for energy storage and adsorption.

A sandwich model of Cr(VI) adsorption and detoxification by Fenton modified chitosan

The Fenton reaction has the advantages of short reaction time, low cost, no toxicity, and straightforward application and control. The Fenton reaction generates highly reactive HO•, which has been applied effectively. However, the effect of the generated Fe³⁺ has not been investigated widely. In this study, the Fenton reaction was used to improve the Cr(VI) adsorption and detoxification capacities of chitosan. After the Fenton modification, chitosan efficiently adsorbed Cr(VI) and transformed it into the less toxic Cr(III) in a wide pH range as a result of layer formation, which was described by a sandwich model. The adsorption of Cr(VI) onto the Fenton modified chitosan was in good agreement with the Freundlich adsorption model, and the adsorption capacity exceeded 120 mg/g. During the Fenton reaction, H₂ O₂ and HO• with high oxidative activity broke the hydrogen bonds in the chitosan structure, resulting in the release of free amine groups for Fe³⁺ to form metal-binding biopolymers. The distance between the chitosan polymers increased, and additional adsorption sites were created. HCrO₄ ^- entered the gap between the chitosan polymer and was adsorbed on the newly created adsorption sites. The sandwich adsorption model indicated that the Fenton modified chitosan provided a high concentration of active sites for Cr(VI) capture and detoxification. PRACTITIONER POINTS: Fenton reaction was used to improve the adsorption ability of chitosan. The formed Fe³⁺ in Fenton reaction was utilized. HO· broke the hydrogen bonds and Fe³⁺ ions chelated with chitosan in modification. Cr(VI) could be adsorbed and reduced efficiently by Fenton modified chitosan. The Fenton modified chitosan provided a high concentration of active sites for Cr(VI) capture and detoxification.

Adsorption of direct yellow brown D3G from aqueous solution using loaded modified low-cost lignite: Performance and mechanism

Low-cost lignite-based, copper-containing adsorbents (Cu-raw) were developed through a simple ultrasonic impregnation protocol for enhanced adsorption of direct yellow brown D3G (DYB) from aqueous solutions while treating copper-containing wastewater. The adsorbent was characterized by X-ray diffraction (XRD), scanning electron microscopy-energy dispersion spectroscopy (SEM-EDS), Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The adsorption isotherms and kinetics were studied, and the factors that affect the adsorption, such as adsorbent dosage and solution pH, were investigated. The results showed that DYB adsorption was highly pH dependent and the isotherm of adsorption could be well described by the Langmuir-Freundlich model and the maximum DYB adsorption capacity was estimated to be 369 mg/g at 25°C. The electrostatic and chelating interactions were the main interfacial interaction mechanism, and the synergetic removal performance of lignite toward cationic metal ions and anionic dye was shown. The kinetic data were well fitted to the pseudo-second-order equation, indicating that chemical sorption was the rate-limiting step. The findings reported in this work highlight the potential of using lignite as an effective low-cost adsorbent for the removal of organic pollutants from wastewater.

A multifunctional gelatine-quaternary ammonium copolymer: An efficient material for reducing dye emission in leather tanning process by superior anionic dye adsorption

Leather wastewater is one of the most polluting industrial emissions. The efficiency of wastewater remediation is limited by its complex composition. Herein, a novel strategy for designing modified gelatine with higher degree of quaternization (MG-2) is presented. The higher degree of quaternization allows sufficient adsorption of dyes in the tanning process. It is an in situ, environmentally friendly, and innovative strategy to limit dye emissions and can circumvent the subsequent waste management. Dyes such as Direct Purple N and Acid Black 24 could be adsorbed completely within 5 min by the MG-2 film formed from MG-2 solution. In addition, a remarkable efficiency in removing Acid Red 73, Golden Orange G, and Acid Orange II (>96.1% removal rates) was achieved within 30 min. The adsorption equilibrium data suggested that the adsorption capacity was positively correlated to the concentration of MG-2. When Acid Orange II and MG-2 were used in the industrial re-tanning process, the residual dye concentration in wastewater was only 23.1 mg L^-1, indicating that MG-2 is a promising re-tanning agent for adsorbing dyes in the leather tanning process.

A new biocompatible ternary Layered Double Hydroxide Adsorbent for ultrafast removal of anionic organic dyes

It would be of great significance to introduce a new biocompatible Layered Double Hydroxide (LDH) for the efficient remediation of wastewater. Herein, we designed a facile, biocompatible and environmental friendly layered double hydroxide (LDH) of NiFeTi for the very first time by the hydrothermal route. The materialization of NiFeTi LDH was confirmed by FTIR, XRD and Raman studies. BET results revealed the high surface area (106 m²/g) and the morphological studies (FESEM and TEM) portrayed the sheets-like structure of NiFeTi nanoparticles. The material so obtained was employed as an efficient adsorbent for the removal of organic dyes from synthetic waste water. The dye removal study showed >96% efficiency for the removal of methyl orange, congo red, methyl blue and orange G, which revealed the superiority of material for decontamination of waste water. The maximum removal (90%) of dyes was attained within 2 min of initiation of the adsorption process which supported the ultrafast removal efficiency. This ultrafast removal efficiency was attributed to high surface area and large concentration of -OH and CO₃²⁻ groups present in NiFeTi LDH. In addition, the reusability was also performed up to three cycles with 96, 90 and 88% efficiency for methyl orange. Furthermore, the biocompatibility test on MHS cell lines were also carried which revealed the non-toxic nature of NiFeTi LDH at lower concentration (100% cell viability at 15.6 μg/ml). Overall, we offer a facile surfactant free method for the synthesis of NiFeTi LDH which is efficient for decontamination of anionic dyes from water and also non-toxic.

Synthesis of Two Mononuclear Schiff Base Metal (M = Fe, Cu) Complexes: MOF Structure, Dye Degradation, H2O2 Sensing, and DNA Binding Property

O-Vanillin and ethylenediamine were used for the synthesis of N,N'-bis(O-vanillinidene)ethylenediamine (O-VEDH2) Schiff base ligand, which was characterized by UV-visible and 1H NMR spectroscopy. The Schiff base ligand O-VEDH2 has been employed to synthesize novel [C18H22FeN2O6]NO3 (1) and C18H16CuN2O5 (2) complexes by the simple slow evaporation method. The single crystals were characterized by X-ray crystallography, as well as Fourier-transform infrared and UV-visible spectroscopy techniques. Complexes 1 and 2 crystallize in monoclinic and orthorhombic space groups with P121/n1 (14) and Pnma (62) point groups, respectively, and both show metal-organic frameworks like structures. Complexes 1 and 2 have optical band gaps of 4.1 and 2.9 eV, respectively, indicating their semiconducting properties. The dye degradation activity and H2O2 sensing of the complexes 1 and 2 were determined in different conditions. The photocatalytic test was performed in the presence of sunlight, methylene blue (MB), and complexes 1 and 2. An interesting result was obtained that complex 2 has degradation ability against MB and the rate constant (K) is 5.46 × 10-5 s-1, whereas complex 1 has H2O2 sensing properties. Both complexes are bound to Calf-thymus DNA by intercalation binding mode, and binding constants (K b) of complexes 1 and 2 are 3.77 × 103 and 1.49 × 104 M-1, respectively.

Polyaniline/attapulgite-supported nanoscale zero-valent iron for the rival removal of azo dyes in aqueous solution

In this paper, polyaniline/attapulgite (PANI/APT)-supported nanoscale zero-valent iron (nZVI) composites were synthesized by liquid-phase chemical reduction method and used for the removal of two kinds of dyes. The structure of as-prepared nZVI/PANI/APT was characterized by various test methods. The removal property and degradation mechanism for azo (alizarin yellow R, methyl red, chrome black T, methyl orange) and non-azo (methylene blue, rhodamine B) dyes in aqueous solution were investigated. The presence of PANI/APT can decrease the aggregation of nZVI particles with maintenance of reactivity and improving adsorption capacity for degradation azo dye. The experiment results showed that the removal property of the composite materials on azo dyes is obviously better than that on non-azo dyes. The varying removal efficiencies of dyes depend on the different degradation mechanisms. Azo dyes removal by nZVI/PANI/APT was mainly due to the reductive cleavage of the N = N of nZVI, while non-azo dyes removal mainly contributes to the adsorption of PANI/APT. The study demonstrated that nZVI/PANI/APT has potential applications for the removal of azo dyes from wastewaters.

Graphene oxide nanocomposite hydrogel based on poly(acrylic acid) grafted onto salep: an adsorbent for the removal of noxious dyes from water

In this study, a graphene oxide nanocomposite hydrogel (GONH) based on poly(acrylic acid) grafted onto a natural salep polysaccharide was synthesized and investigated as an adsorbent for the removal of cationic dye from aqueous solution.

Preparation and properties of chitosan-metal complex: Some factors influencing the adsorption capacity for dyes in aqueous solution

Chitosan-metal complexes have been widely studied in wastewater treatment, but there are still various factors in complex preparation which are collectively responsible for improving the adsorption capacity need to be further studied. Thus, this study investigates the factors affecting the adsorption ability of chitosan-metal complex adsorbents, including various kinds of metal centers, different metal salts and crosslinking degree. The results show that the chitosan-Fe(III) complex prepared by sulfate salts exhibited the best adsorption efficiency (100%) for various dyes in very short time duration (10min), and its maximum adsorption capacity achieved 349.22mg/g. The anion of the metal salt which was used in preparation played an important role to enhance the adsorption ability of chitosan-metal complex. SO₄^2- ions not only had the effect of crosslinking through electrostatic interaction with amine group of chitosan polymer, but also could facilitate the chelation of metal ions with chitosan polymer during the synthesis process. Additionally, the pH sensitivity and the sensitivity of ionic environment for chitosan-metal complex were analyzed. We hope that these factors affecting the adsorption of the chitosan-metal complex can help not only in optimizing its use but also in designing new chitosan-metal based complexes.

Al-Doped chitosan nonwoven in a novel adsorption reactor with a cylindrical sleeve for dye removal: performance and mechanism of action

To overcome the inconvenience of solid/liquid separation of powdered adsorbents, a novel adsorption reactor with a cylinder sleeve was designed to match the textile-pattern of chitosan nonwoven for the sake of easy separation and simple operation.

Adsorption behavior of one-dimensional coordination polymers [Cu(bipy)X]n (X = 2Cl− and SO42−) toward acid orange 7 and methyl orange

A kind of one-dimensional coordination polymer, [Cu(bipy)X]_n (X = 2Cl⁻ or SO₄²⁻), was prepared by Cu²⁺ and 4,4′-bipyridine (bipy) through a facile method, and used as the adsorbent for removal of acid orange 7 (AO7) and methyl orange (MO) from water.

Enhanced removal of methylene blue and methyl violet dyes from aqueous solution using a nanocomposite of hydrolyzed polyacrylamide grafted xanthan gum and incorporated nanosilica

The synthesis and characterization of a novel nanocomposite is reported that was developed as an efficient adsorbent for the removal of toxic methylene blue (MB) and methyl violet (MV) from aqueous solution. The nanocomposite comprises hydrolyzed polyacrylamide grafted onto xanthan gum as well as incorporated nanosilica. The synthesis exploits the saponification of the grafted polyacrylamide and the in situ formation of nanoscale SiO2 by a sol-gel reaction, in which the biopolymer matrix promotes the silica polymerization and therefore acts as a novel template for nanosilica formation. The detailed investigation of the kinetics and the adsorption isotherms of MB and MV from aqueous solution showed that the dyes adsorb rapidly, in accordance with a pseudo-second-order kinetics and a Langmuir adsorption isotherm. The entropy driven process was furthermore found to strongly depend on the point of zero charge (pzc) of the adsorbent. The remarkably high adsorption capacity of dyes on the nanocomposites (efficiency of MB removal, 99.4%; maximum specific removal Qmax, 497.5 mg g(-1); and efficiency of MV removal, 99.1%; Qmax, 378.8 mg g(-1)) is rationalized on the basis of H-bonding interactions as well as dipole-dipole and electrostatic interactions between anionic adsorbent and cationic dye molecules. Because of the excellent regeneration capacity the nanocomposites are considered interesting materials for the uptake of, for instance, toxic dyes from wastewater.

Adsorption studies of methyl orange on an immobilized Mn-nanoparticle: kinetic and thermodynamic

A nano-adsorbent containing Mn-nanoparticle decorated SiO₂–Al₂O₃ was developed. The application of the nano-adsorbent was studied to remove methyl orange. It effectively removes 98% of methyl orange from contaminated water after 15 min. The novel nano-adsorbent was very stable and easily separated from the purified water.

An integrative technique based on synergistic coremoval and sequential recovery of copper and tetracycline with dual-functional chelating resin: roles of amine and carboxyl groups

A novel chelating resin (R-AC) bearing dual-functional groups (amino and carboxyl groups) was self-synthesized and it showed superior properties on synergistic coremoval of Cu(II) and tetracycline (TC) to commercial resins (amine, carboxyl, and hydrophobic types), which was deeply investigated by equilibrium and kinetic tests in binary, preloading, and saline systems. The adsorption of TC on R-AC was markedly enhanced when coexisted with Cu(II), up to 13 times of that in sole system, whereas Cu(II) uptake seldom decreased in the copresence of TC. Decomplexing-bridging, which included [Cu-TC] decomplexing and [R-Cu] bridging for TC, was demonstrated as the leading mechanism for the synergistic coremoval of Cu(II) and TC. Carboxyl groups of R-AC played a dominant role in decomplexing of [Cu-TC] complex and releasing free TC. Cu(II) coordinated with amine groups of R-AC was further proved to participate in bridging interaction with free TC, and the bridging stoichiometric ratio ([NH-Cu]: TC) possibly was 2:1. About 96.9% of TC and 99.3% of Cu could be sequentially recovered with dilute NaOH followed by HCl. Considering stable application for five cycles in simulated and practical wastewater, R-AC shows great potential in green and simple coremoval of antibiotic and heavy metal ions.

Insight into highly efficient coremoval of copper and p-nitrophenol by a newly synthesized polyamine chelating resin from aqueous media: competition and enhancement effect upon site recognition

Highly efficient coremoval of Cu(II) and p-nitrophenol (PNP) was accomplished using a newly synthesized polyamine chelating resin (CEAD) as compared to three other commercial resins. The mutual effects and inner mechanisms of their adsorption onto CEAD were systematically investigated by binary, preloading, thermodynamic, and dynamic adsorption procedures. PNP was adsorbed onto both hydrophobic and hydrophilic sites, while Cu(II) only interacted with hydrophilic amine group sites. In both preloading and binary systems, the adsorption of PNP was inhibited to the same degree by the presence of Cu(II) because of selective recognition and direct competition. On the other hand, the presence of PNP obviously enhanced the adsorption of Cu(II) by more than 7%, which was related to PNP loading on the hydrophobic surface. As proved by structural characterization, hydroxyl groups facing outward create new sites for coordination with Cu(II). Moreover, ionic strength exerted some positive influence on the properties of CEAD. Finally, more than 98% of PNP and 99% of Cu(II) could be sequentially recovered with dilute NaClO3 and HCl. These superior properties demonstrated with CEAD indicate that it could be applied to wastewaters containing both heavy metals and PNP, even for high saline aqueous media.

Highly efficient detoxification of Cr(VI) by chitosan-Fe(III) complex: process and mechanism studies

Metal-biopolymer complexes has recently gained significant attention as an effective adsorbent used for the removal of Cr(VI) from water. Unfortunately, despite increasing research efforts in the field of removal efficiency, whether this kind of complex can reduce Cr(VI) to less-toxic Cr(III) and what are the mechanisms of detoxification processes are still unknown. In this study, despite the highly adsorption efficiency (maximum adsorption capacity of 173.1 mg/g in 10 min), the significant improvement of Cr(VI) reduction by chitosan-Fe(III) complex compared with normal crosslinked chitoan has been demonstrated. In addition, the structure of chitosan-Fe(III) complex and its functional groups concerned with Cr(VI) detoxification have been characterized by the powerful spectroscopic techniques X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS). The XPS spectra indicated that the primary alcoholic function on C-6 served as an electron donor during Cr(VI) reduction and was oxidized to a carbonyl group. The X-ray adsorption near edge spectra (XANES) of the Cr(VI)-treated chitosan-Fe(III) complex revealed the similar geometrical arrangement of Cr species as that in Cr(III)-bound chitosan-Fe(III). Overall, a possible process and mechanism for highly efficient detoxification of Cr(VI) by chitosan-Fe(III) complex has been elucidate.

Interaction of organic contaminants with natural clay type geosorbents: potential use as geologic barrier in urban landfill

The aim of this work is to characterize the capability of several clay materials as preservative of organic pollution for use as landfill barrier. Interaction of representative organic pollutants with different polarity and water solubility (atrazine, benzamide, methomyl, paraquat and toluene) with several clay materials coming from several locations of Spain were studied. Batch suspension method was used to study the pesticide adsorption onto the clay sorbents in solution conditions that simulate the composition of a young leachate in its aerobic acetogenic stage (pH=5 and I=0.15) The obtained data of the analytes sorption were modelized by several sorption isotherm models, and the best fitted data were got with a generalized Langmuir adsorption isotherm. The higher maxima adsorptions were observed for paraquat (50-62 mmol kg(-1)) and toluene (19-34 mmol kg(-1)) whereas more hydrophobic compounds present lower adsorption (0.7-2.5 mmol kg(-1)). Paraquat is the compound that presents the higher bonding coefficients. Therefore these clays could be used as components of the multibarriers in controlled urban landfill.

Fast and highly efficient removal of dyes under alkaline conditions using magnetic chitosan-Fe(III) hydrogel

The dyeing effluent of high alkalinity, which could not be treated efficiently by traditional wastewater technologies, highlighted the need to explore a technically feasible, highly efficient and cost effective method. Thus, a fast and highly efficient method for the removal of dyes under alkaline conditions using magnetic chitosan-Fe(III) hydrogel was proposed. Firstly, chitosan-Fe(III) hydrogel was prepared by a chelation procedure with cheap and environmentally friendly chitosan and iron salts. We characterized the sorption and desorption of C. I. Acid Red 73, a common type of anionic dye, on magnetic chitosan-Fe(III) hydrogel, to understand its availability for alkaline dyeing wastewater. Sorption of dye to chitosan-Fe(III) hydrogel was fast (adsorption could reach equilibrium in less than 10 min) in a wide pH range, and agreed well to the Langmuir-Freundlich adsorption model with a high maximum adsorption capacity of 294.5 mg/g under pH = 12. Meanwhile, 1 mol/L NaOH was used to desorb the dye efficiently (desorption efficiency 94.4%) and 0.1 mol/L HCl was applied to regenerate the chitosan-Fe(III) hydrogel. The results showed that the chitosan-Fe(III) hydrogel could retain its high efficiency after the desorption and regeneration. The common coexisting ions almost had no negative effect on the dye adsorption of chitosan-Fe(III) and the removals of a variety of anionic dyes suggest that the magnetic chitosan-Fe(III) hydrogel could efficiently adsorb both the acid and reactive dyes under alkaline condition. Overall, the results reported herein indicated that magnetic chtisoan-Fe(III) with high adsorption efficiency and strong magnetic property is very attractive and implies a potential of practical application for alkaline dyeing effluent treatment.

Application of dithiocarbamate-modified starch for dyes removal from aqueous solutions

The present study shows that the dithiocarbamate-modified starch (DTCS) is a commercially promising sorbent for the removal of anionic dyes from aqueous solutions. It is more effective than activated carbon for this purpose. At the appropriate solution pH of 4, kinetic studies indicate that the sorption of the dyes tends to follow pseudo-first-order equation. The sorption equilibrium is best described by the Langmuir-Freundlich isotherm model at 298 K. The capacities for individual dyes follow the sequence acid orange 7 > acid orange 10 > acid red 18 > acid black 1 > acid green 25, which is consistent with the inverse order of molecular size. The negative enthalpy change for the adsorption process confirms the exothermic nature of adsorption, and a free energy change confirms the spontaneity of the process. The FT-IR spectra and thermogravimetric analyses verify the sorption based on starch-NH(2)(+)CSSH⋯(-)O(3)S-dye electrostatic attraction. The DTCS can be regenerated from the dye loaded DTCS in a weak basic solution containing sodium sulfate.

Behaviors and mechanism of acid dyes sorption onto diethylenetriamine-modified native and enzymatic hydrolysis starch

In this paper, different starches were modified by diethylenetriamine. The native starch reacted with diethylenetriamine giving CAS, whereas the enzymatic hydrolysis starch was modified by diethylenetriamine producing CAES. Adsorption capacities of CAES for four acid dyes, namely, Acid orange 7 (AO7), Acid orange 10 (AO10), Acid green 25 (AG25) and Acid red 18 (AR18) have been determined to be 2.521, 1.242, 1.798 and 1.570 mmol g(-1), respectively. In all cases, CAES has exhibited higher sorption ability than CAS, and the increment for these dyes took the sequence of AO7 (0.944 mmol g(-1))>AO10 (0.592 mmol g(-1))>AR18 (0.411 mmol g(-1))>AG25 (0.047 mmol g(-1)). Sorption kinetics and isotherms analysis showed that these sorption processes were better fitted to pseudo-second-order equation and Langmuir equation. Chemical sorption mechanisms were confirmed by studying the effects of pH, ionic strength and hydrogen bonding. Thermodynamic parameters of these dyes onto CAES and CAS were also observed and it indicated that these sorption processes were exothermic and spontaneous in nature.