Adsorption of Pb2+ and Cd2+ on the l-cysteine-functionalized graphene oxide/chitosan/polyvinyl alcohol hydrogel: Kinetic,isotherm, and thermodynamic study

In this study, polyvinyl alcohol-chitosan-cysteine-functionalized graphene oxide (PCCFG) hydrogel was synthesized from l -cysteine-functionalized graphene oxide (CFG), chitosan (CS), and polyvinyl alcohol (PVA). The hydrogel was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy and employed for removing lead ion (Pb²⁺) and cadmium ion (Cd²⁺) from aqueous solution. The effects of initial metal ion concentration, hydrogel dose, pH, time, and temperature were studied. The experimental data were well described by a pseudo-second-order kinetic model and Langmuir isotherm with maximum adsorption capacities of 250 and 192 mg g⁻¹ at 25°C for Pb²⁺ and Cd²⁺, respectively. The adsorption capacity of the PCCFG hydrogel increased with an increase in temperature. The value of ∆G° was negative, which shows the spontaneity of the reaction (electron exchange or ion exchange) between the metal ion and electron-rich atoms (–N, –S, –O). The positive ∆H° shows that the adsorption reaction consumes energy and the positive ∆S° shows the strong affinity of PCCFG toward the Pb²⁺ and Cd²⁺ ions. Pb²⁺ had better affinity and less spontaneity than Cd²⁺. The results show that the coexistence of Pb²⁺, Cd²⁺, and Cu²⁺ in the solution inhibits the adsorption capacity of PCCFG.     

Synthesis,Characterization and Environmental Applications of a New Bio-Composite Gelatin-Zr(IV) Phosphate

Gelatin-Zr(IV) phosphate composite (GT/ZPC) was synthesized by sol–gel method. Different techniques viz. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray powdered diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for the characterisation of GT/ZPC composite ion exchanger. The ion exchange capacity (IEC) of GT/ZPC was observed to be better (1.04 meq g^?1) than its inorganic counterpart (0.64 meq g^?1). The pH studies revealed the monofunctional nature of GT/ZPC with one inflection point. The distribution studies showed that the GT/ZPC was highly selective for Cd²⁺ as compare to other metal ions. The environmental applicability of ion exchanger has been analysed for binary separations of metal ions using column method. Cd²⁺ was effectively removed from synthetic mixture of metal ions (Zn²⁺, Pb²⁺, Ni²⁺, Co²⁺ and Cu²⁺).     

Poultry litter-based activated carbon for removing heavy metal ions in water

Utilization of poultry litter as a precursor material to manufacture activated carbon for treating heavy metal-contaminated water is a value-added strategy for recycling the organic waste. Batch adsorption experiments were conducted to investigate kinetics, isotherms, and capacity of poultry litter-based activated carbon for removing heavy metal ions in water. It was revealed that poultry litter-based activated carbon possessed significantly higher adsorption affinity and capacity for heavy metals than commercial activated carbons derived from bituminous coal and coconut shell. Adsorption of metal ions onto poultry litter-based carbon was rapid and followed Sigmoidal Chapman patterns as a function of contact time. Adsorption isotherms could be described by different models such as Langmuir and Freundlich equations, depending on the metal species and the coexistence of other metal ions. Potentially 404 mmol of Cu²⁺, 945 mmol of Pb²⁺, 236 mmol of Zn²⁺, and 250–300 mmol of Cd²⁺ would be adsorbed per kg of poultry litter-derived activated carbon. Releases of nutrients and metal ions from litter-derived carbon did not pose secondary water contamination risks. The study suggests that poultry litter can be utilized as a precursor material for economically manufacturing granular activated carbon that is to be used in wastewater treatment for removing heavy metals.     

Itaconic Acid Grafted Starch Hydrogels as Metal Remover: Capacity,Selectivity and Adsorption Kinetics

Hydrogels were synthesized by free radical graft copolymerization of itaconic acid (IA) onto corn starch (S-g-IA). For this purpose, potassium permanganate (KMnO₄)-sodium bisulfite (NaHSO₃) was used as redox initiation system. The formation of grafted starches was confirmed by Fourier transform infrared spectroscopy, wide angle X-ray scattering, thermogravimetric analysis and scanning electron microscopy. The effect of monomer concentration, neutralization, addition of crosslinking agent, N,N-bismetilenacrilamide (MBAm), and initiator concentration on grafting efficiency and adsorption capacity of the starch hydrogels was investigated. It was demonstrated that the introduction of carboxyl and carbonyl groups promoted starch hydration and swelling. Grafting degree increased with the decrease of monomer concentration, increase of initiator concentration, grade of neutralization and the addition of MBAm without neutralization. Remarkably the resulting materials exhibited water absorption capacities between 258 and 1878% and the ability to adsorb metal ions. It was experimentally confirmed the metal uptake, obtaining the higher adsorption capacity (q _e  = 35 mg/g) for the product prepared with the pre-oxidation and lower initiator concentration. The removal capacity order was Pb²⁺>Ni²⁺>Zn²⁺>Cd²⁺. Moreover, the experimental kinetic and the equilibrium adsorption data for Ni²⁺ and Pb²⁺ were best fitted to the pseudo-second order and Freundlich isotherm models, respectively. This work describes for the first time the preparation of metal removal hydrogels based on starch and itaconic acid using the pair redox system KMnO₄/NaHSO₃, which avoids the starch hydrolysis and allows itaconic acid grafting incorporation without the requirement of more reactive comonomers.     

Adsorption characteristics of Cu2+ and Zn2+ from aqueous solution using carbonized food waste

The aim of the present study was to analytically provide adsorption characteristics of Cu²⁺ and Zn²⁺ using carbonized food waste (CFW); more specifically, batch tests were conducted using various concentrations of metal ions, contact times, and initial pH levels in an attempt to understand the adsorption removal of heavy metal ions in aqueous solution at concentrations ranging between 50 and 800 mg/l. The results confirmed that the adsorption equilibrium was established within a maximum of 80 min, and the maximum concentrations for adsorption of Cu²⁺ and Zn²⁺ were 28.3 and 23.5 mg/g, respectively. These adsorption levels indicate that CFW has better performance than many other adsorbents. In experiments using different pH conditions, the applicability to acid wastewater was found to be high, and an excellent adsorption removal ratio of 75%–90% was observed under acid conditions at pH 2–4. Furthermore, as the adsorption time increased, the calcium component in the CFW began to leach into the aqueous solution and raise the pH, accordingly causing the removal of heavy metal ions partially as a result of precipitation. When our results were analyzed using the Langmuir model and the Freundlich model for isothermal adsorptivity, the activity of CFW in this study was shown to be more consistent with the former; the adsorption speed of Cu²⁺ and Zn²⁺ according to a pseudosecond-order reaction model was found to be very fast for an initial concentration of not more than 100 mg/l. In a test in which an attempt was made to compare adsorption capacity values obtained from the experiments in this study with the aforementioned three models, the pseudosecond-order reaction model was found to provide results closest to the actual values.     

Adsorption Efficiency of Polyaspartate-Montmorillonite Composite Towards the Removal of Pb(II) and Cd(II) from Aqueous Solution

The selective modification of sodium montmorillonite (Na⁺-Mt) surface with polyionene followed by poly (succinimde-co-aspartate) has been considered. Na⁺-Mt was allowed to react with well characterized polyionene in two fold excess. The resulting polyionene/Mt (IC) was further modified with poly (succinimide-co-aspartate) through an ion exchange process. The obtained polyaspartate/Mt (IPS) composite was characterized by elemental analysis, X-ray diffraction, FTIR spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and BET surface analyzer. The adsorption efficiency of IPS composite was investigated for the removal of Pb(II) and Cd(II) from aqueous solution under different experimental conditions including initial metal ions concentration, temperature and single and binary mixture systems of metal ions. The experimental data were analyzed by Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models. Langmuir model reveals that the monolayer adsorption capacity of IPS was 92.59 and 67.57 mg/g for Pb(II) and Cd(II), respectively. The modification of parent Na⁺-Mt enhanced their adsorption capacity by about 87.91 and 29.84% for Pb(II) and Cd(II), respectively, due to inclusion of extra active sites of polyaspartate. The mean sorption energy, E calculated from Dubinin–Radushkevich isotherm were 2.75 and 1.98 kJ/mol for the adsorption of Pb(II) and Cd(II), respectively, indicating physical adsorption process. Also, The thermodynamic parameters were calculated and indicated that the adsorption was spontaneous and exothermic process. The mechanism of cation exchange and complexation of metal ions was suggested. IPS composite has a considerable potential for the removal of heavy metal ions from aqueous solution and wastewater stream.     

Immobilization of copper ions laden kaolin waste: influence of thermal treatment on its immobilization in cement paste

This work aims to study the influence of thermal treatment of Cu²⁺ laden kaolin wastes on its immobilization efficiency in cement paste. Compressive strength and toxicity characteristic leaching procedure (TCLP) of 5–20 % kaolin waste blended cement pastes were tested. X-ray diffraction (XRD) results illustrate that adsorption of Cu²⁺ ions modify the crystal structure of kaolinite mineral. Fourier transform infrared (FTIR) results indicate that the adsorption sites on the kaolin surface that were occupied with free water molecules have been replaced with Cu²⁺ ions adsorbed from aqueous solutions. The thermal treatment of kaolin waste improves fixation ratio of Cu²⁺ in cement pastes containing up to 20 % of thermally treated waste. This is due to: pozzolanic activity of calcined kaolin, conversion of leachable adsorbed Cu²⁺ ions into encapsulated unleachable phase that does not retard the hydration of cement as well as adsorption of much of leachable Cu²⁺ ions on surfaces of hydration products and occlusion in its lattice structure as illustrated from XRD, FTIR, thermogravimetric, scanning electron microscopy and TCLP results. The fixation ratio of Cu²⁺ in cement paste blended with 20 % of thermally treated kaolin waste, reaches maximum value of about 97 % compared to 82 % for cement paste blended with 20 % of untreated kaolin waste.     

Adsorption of Ammonium by Graphene Oxide-Based Composites Prepared by UV Irradiation and Using as Slow-Release Fertilizer

A novel sodium alginate-grafted poly(acrylic acid)/graphene oxide (NaAlg-g-PAA/GO) composite hydrogel was prepared via ultraviolet irradiation, and characterized by infrared spectroscopy spectrometer. X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. It was employed to adsorb NH₄⁺ from aqueous solution and used as slow-release nitrogen fertilizers (SNFs). Result indicated that the adsorption process for NH₄⁺ reached equilibrium within 50 min, with the adsorption capacity of 6.6 mmol g^?1 even if 30 wt% GO was incorporated. The results of adsorption kinetic and isotherm were well described by the pseudo-second-order and Freundlich model. The thermodynamics analysis showed the adsorption process was spontaneous. The study indicated excellent water-holding ratio of soil with 2 wt% SNFs was 81.2%, and nitrogen release was up to 55.1% within 40 days in soil. Overall, NaAlg-g-PAA/GO could be considered as an efficient adsorbent for the recovery of nitrogen with the agronomic reuse as a fertilizer.     

Enzyme-Assisted Extraction and Pb<Superscript>2+</Superscript> Biosorption of Polysaccharide from <Emphasis Type="Italic">Cordyceps militaris</Emphasis>

The enzyme assisted extraction conditions of polysaccharide from Cordyceps militaris mycelia were firstly investigated by kinetics analysis and the optimal operating was found to be: extraction temperature 40 °C; solid-solvent ratio 1:20; extraction pH 4.0; cellulase concentration 2.0%. The polysaccharide extraction yield was 5.99% under these optimized conditions. Furthermore, a fundamental investigation of the biosorption of Pb²⁺ from aqueous solution by the C. militaris polysaccharide was performed under batch conditions. The suitable pH (5.0), polysaccharide concentration (0.20 g L^?1), initial Pb²⁺ concentration (300 mg L^?1) and contact time (40 min) were outlined to enhance Pb²⁺ biosorption from aqueous medium. The Langmuir isotherm model and pseudo first order kinetic model fitted well to the data of Pb²⁺ biosorption, suggesting the biosorption of Pb²⁺ onto C. militaris polysaccharide was monolayer biosorption and physical adsorption might be the rate-limiting step that controlled the adsorption process. FTIR analysis showed that the main functional groups of C. militaris polysaccharide involved in adsorption process were carbonyl, carboxyl, and hydroxyl groups.     

Synthesis,Characterization and Application of α, β, and γ Cyclodextrin-Conjugated Graphene Oxide for Removing Cadmium Ions from Aqueous Media

In this study, a novel and facile route for the synthesis of cyclodextrin-conjugated graphene oxide (CDs–GO) nanocomposites by esterification reaction in the presence of EDC/DMAP as catalyst, was developed. The formation of CDs–GO was successfully approved by FT-IR, SEM, TEM, TGA and BET analyses. Then competitive adsorption capacity of cadmium ion by CDs–GO composites and the impact of different empirical parameters like contact time, initial metal ion concentration, and initial pH on the adsorption process were studied. The results showed that β-CD–GO at pH 7 is suitable for removing Cd(II) with 90?% removal efficiency. Also, the adsorption capacity experiment at constant concentration of 50 ppm of Cd(II) showed that more than 50?% of Cd(II) ions could be adsorbed by γ-CD–GO reaching an equilibrium within 2 h. Therefore, the γ-CD–GO and α-CD–GO showed high adsorption capacity toward Cd²⁺ (222.22 mg/g) which were pointedly more than that of β-CD–GO (208.33 mg/g). Furthermore, adsorption kinetics, isotherm studies, and thermodynamic analyses were evaluated. The adsorption data exhibited excellent fit to the pseudo-second-order (R²?>?0.99) and Freundlich isotherm models.

     

Adsorption studies of caesium on zirconium molybdoarsenate (ZrMAs)

The applicability of zirconium molybdoarsenate (ZrMAs) for efficient removal of Cs from aqueous solution by adsorption has been investigated. The kinetics of adsorption of caesium ions has been studied by using radioanalytical procedure over a concentration range (10⁻⁴−10⁻² mol dm⁻³) and in the temperature range (303–318 K). The results showed that the uptake follows the first order rate law with respect to caesium concentration and obeys Langmuir and Modified Freundlich adsorption isotherms in the concentration studied. The effect of temperature on adsorption equilibrium has been studied and the thermodynamic quantities (ΔH^o, ΔG^o and ΔS^o) has been evaluated. They showed that the process is exothermic in nature.     

Selection of adsorbents for treatment of leachate: batch studies of simultaneous adsorption of heavy metals

The simultaneous adsorption of copper (Cu), cadmium (Cd), nickel (Ni), and lead (Pb) ions from spiked deionized water and spiked leachate onto natural materials (peat A and B), by-product or waste materials (carbon-containing ash, paper pellets, pine bark, and semi-coke), and synthetic materials (based on urea-formaldehyde resins, called blue and red adsorbents) or mixtures thereof was investigated. The adsorbents that gave the highest metal removal efficiencies were peat A, a mixture of peat B and carbon-containing ash, and a mixture of peat A and blue. At an initial concentration of 5 mg/l for each metal, the removal of each species of metal ion from spiked water and spiked leachate solutions was very good (>90%) and good (>75%), respectively. When the initial concentration of each metal in the solutions was twenty times higher (100 mg/l), there was a noticeable decrease in the removal efficiency of Cu²⁺, Cd²⁺, and Ni²⁺, but not of Pb²⁺. Langmuir monolayer adsorption capacities, q_m, on peat A were found to be 0.57, 0.37, and 0.36 mmol/g for Pb²⁺, Cd²⁺, and Ni²⁺, respectively. The order of metal adsorption capacity on peat A was the same in the case of competitive multimetal adsorption conditions as it was for single-element adsorption, namely Pb²⁺ > Cd²⁺ ≥ Ni²⁺. The results show that peat alone (an inexpensive adsorbent) is a good adsorbent for heavy metal ions.     

Investigation of the Thermosensitive Nanosphere Polymer in Removing Organophosphorus Pesticides from Water and Its Isotherm Study (Case Study: Diazinon)

In this research, a novel thermosensitive nanosphere polymer (TNP) was synthesized by copolymerization of N-isopropylacrylamide with 3-allyloxy-1,2-propanediol for the removal of diazinon from water. The characterization of the synthesized adsorbent has been performed by Fourier transform infrared spectrometer, scanning electron microscopy and elemental analysis. Batch adsorption method was performed to investigate the influences of various parameters like pH, temperature and contact time on the adsorption of diazinon. The equilibrium adsorption data of diazinon by TNP was studied by Langmuir, Freundlich, Temkin and Redlich–Peterson model. According to equilibrium adsorption results, the Langmuir, Freundlich and Temkin constants were evaluated to be 0.912 (L/mg), 7.916 (mg/g) (L/mg)^1/n and 2.494 respectively at pH 7 and room temperature. Based on Redlich–Peterson model analysis, the equilibrium data for the adsorption of diazinon was conformed well to the Langmuir isotherm model. This method was successfully applied for removal of diazinon from environmental samples. Moreover, in reusing of TNP, the sorption capacity was maintained without any significant change after 10 cycles of sorption–desorption process.     

Adsorptive Removal of Malachite Green Chloride and Reactive Red-198 from Aqueous Solutions by Using Multiwall Carbon Nanotubes-Graft-Poly (2-acrylamido-2-methyl-1-propanesulfonic acid)

The multiwall carbon nanotubes (MWCNTs) were modified by 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) via grafting reaction and γ-rays of ⁶⁰Co source was used as initiator. The outcome product was called hydroxyethylated (HOEt-MWCNTs) graft poly(AMPS) and abbreviated as HOEt-MWCNTs-g-PAMPS. The parameters that affected the grafting yield were optimized. The maximum grafting obtained was ~20 %. HOEt-MWCNTs-g-PAMPS were characterized by Fourier transform infra red, scanning electron microscopy, high resolution transmission electron microscopy, thermal gravimetric analysis. The adsorptive removals of malachite green chloride (MGC) and reactive red 198 (RR-198) onto HOEt-MWCNTs-g-PAMPS were studied at variable conditions. The adsorption isotherms were analyzed using Langmuir, Redlich–Peterson, Freundlich, Khan and Sips models. The results referred that Sips model is the best fitting to adsorption of MGC and Freundlich model is the best fitting to RR-198 adsorption. The monolayer coverage capacities of HOEt-MWCNTs-g-PAMPS for MGC and RR-198 dyes were found 172 and 323 mg g^?1, respectively. The rate of kinetic adsorption processes of MGC and RR-198 onto HOEt-MWCNTs-g-PAMPS were described by using pseudo-first order, pseudo-second order and intraparticle diffusion models. The pseudo-first order and pseudo-second order models were the best choice among the kinetic models to depict the adsorption behaviors of MGC and RR-198 dyes onto HOEt-MWCNTs-g-PAMPS, respectively. Further, the effect of temperature on the adsorption isotherms was investigated and the thermodynamic parameters were obtained. The results indicated that the adsorption process is spontaneous and endothermic. The values of ΔG° varied in range with the mean values showing a gradual increase from ?3.17 to ?3.64 kJ mol^?1 for MGC and ?3.36 to ?3.73 kJ mol^?1 for RR-198. The reusability and regeneration of adsorbent were investigated. The outcome data referred to that the efficiency of adsorbent >98 %. The outline results declared that there is a good potentiality for the HOEt-MWCNTs-g-PAMPS to be used as an adsorbent for the removal of MGC and RR-198 from aqueous solutions.     

Design parameters for fixed bed reactors of activated carbon developed from fertilizer waste for the removal of some heavy metal ions

Activated carbon, developed from fertilizer waste, has been used for the removal of Hg²⁺, Cr⁶⁺, Pb²⁺, and Cu²⁺. Mass transfer kinetic approach has been successfully applied for the determination of various parameters necessary for designing a fixed-bed absorber. Parameters selected are the length of the (PAZ) primary adsorption zone (δ), total time involved for the establishment of primary adsorption zone (t_x), mass rate of flow to the absorber (F_m), time for primary adsorption zone to move down its length (t_δ), amount of adsorbate adsorbed in PAZ from breakpoint to exhaustion (M_s), fractional capacity (f), time of initial formation of PAZ (t_f) and per cent saturation of column at break point. Chemical regeneration has been achieved with 1 M HNO₃.     

Partial characterization of the exopolysaccharide from Oscillatoria trichoides Szafer and the role of released polysaccharide in sequestration of Cr6+

The structural investigation and the chromium adsorptive potential of an exopolysaccharide (EPS) released during the growth of an indigenous cyanobacterium, Oscillatoria trichoides Szafer, were investigated in a laboratory‐scale study. The results showed that, of the total EPS produced, 410.53 milligrams/gram (mg g^?1) were released polysaccharides (RPS) and 11.36 mg g^?1 were capsular polysaccharides (CPS). The sorption of hexavalent chromium (Cr⁶⁺) by the RPS achieved a maximum amount of metal removal (q_max) value of 76.92 mg g^?1 of polysaccharide dry weight. The highest coefficient of determination (0.9742) for the Langmuir adsorption model indicates best fitness of the model in explaining the sorption as a unilayer process. Equilibrium studies indicated that 30 to 40 milligrams per liter initial chromium concentration and a pH of 2 were optimal for biosorption of chromium by the RPS. Scanning electron microscopy with energy‐dispersive X‐ray spectroscopy analysis of Cr⁶⁺‐treated RPS showed the presence of 3.76% bound chromium. Compositional analysis of the EPS showed the presence of carbohydrates, proteins, pyruvic acid, and hexosamines. High‐performance liquid chromatography analysis demonstrated the presence of hexoses, as neutral sugars and glucuronic acid as an acidic sugar. The presence of carboxylic groups was also detected by infrared spectroscopy. The presence of these chemical constituents may serve as binding sites for the metal ions; therefore, the RPS of this species appears to be a promising biosorbent for Cr⁶⁺.     

Chelating Ability and Microbial Stability of an <Emphasis Type="SmallCaps">l</Emphasis>-Arginine-Modified Chitosan-Based Environmental Remediation Material

To improve the heavy metal ion chelating ability and the microbiological stability of chitosan (CS), l-arginine (l-Arg) was grafted on CS polymer in the presence of the condensing agent 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) and the coupling reagent N-hydroxysuccinimide (NHS) to prepare a natural polymer-based environmental rehabilitation material: l-arginine-grafted chitosan (CA). The graft mechanism is discussed, and the reaction conditions were optimized. The product was characterized using elemental analysis, infrared spectroscopy (FT-IR) and ¹³C-NMR spectroscopy (¹³C-NMR). The optimal reaction conditions were a reactant molar ratio nCS:nArg:nEDC:nNHS of 3:3:3:1, a reaction time of 12 h, and a reaction system pH?=?5. Under these conditions, the grafting ratio (GR) was 16.85%, while the product yield (PY) was 90.48%. The results of the adsorption experiments showed that the CA (GR?=?16.85%) had a better removal capacity for highly concentrated Cu²⁺ and Ni²⁺ ions than CS. The antibacterial activity of the CA was also enhanced. When the GR reached 16.85%, the CA almost completely inhibited the growth of colibacillus and Staphylococcus aureus. Due to its high chelating ability and microbiological stability, this novel metal-ion adsorption material, CA, can be considered to have broad application potential in heavy metal ion-polluted water and soil remediation.     

Polymer Supported Calix[4]Arene Derivatives for the Extraction of Metals and Dichromate Anions

Three newly synthesized polymer supported calix[4]arene ionophores (7–9) were synthesized, and their ion binding properties toward selected alkali (Li⁺, Na⁺, K⁺, Cs⁺) and transition metal (Hg²⁺, Ni²⁺, Cu²⁺, Co²⁺, Cd²⁺, and Pb²⁺) cations were investigated. It has been observed that these ionophores are not selective toward a particular metal cation but show better ion binding property as compared to monomeric calixarene derivatives (2 and 6). Ionophore 6 and its supported polymer were also employed in dichromate anion extraction experiments. The polymeric ionophore (9) was found an effective extractant for dichromate anion even at pH 7.     

Enhancement of Sedimentation Velocity of Heavy Metals Loaded Hydroxyapatite Using Chitosan Extracted from Shrimp Waste

In this study, synthesize hydroxyapatite (HA) suspensions sedimentation was used after usual terms as support for adsorption of heavy metals ions. Thus, the effectiveness of chitosan, produced from shrimp waste, in the flocculation of turbid suspensions resulting from the treatment of water contaminated with heavy metals was studied by adsorption on HA. Different particles sizes of HA were mainly controlled in this work (an average of granule size ranging from 1.6 to 63 μm). The results of Cu²⁺ and Zn²⁺ adsorption on HA showed relatively fast kinetics, with removal extent of 88–95 % by varying the initial total metal concentration. High removal rates were obtained for Cu²⁺. Chitosan was found to be able to eliminate by flocculation more than 98 % of turbid suspensions generated by metals adsorption on HA after only 30 min of sedimentation. Effects of pH and dose of chitosan on the coagulation–flocculation process were also studied. The optimal dose of chitosan was found between 0.2 and 2 mg/L which corresponds to an optimal pH ranging from 6 to 7.     

Synthesis of Gum Acacia Capped Polyaniline-Based Nanocomposite Hydrogel for the Removal of Methylene Blue Dye

In this research work, a novel gum acacia capped polyaniline-based nanocomposite hydrogel (GPA NCHs) was developed and evaluated for the adsorptive removal of cationic methylene blue dye (MB) from aqueous solutions. Firstly, Gum acacia (GA) capped Polyaniline (PANI) dispersion was synthesized by using dispersion polymerization. Then, a water-swellable hydrogel network consisting of GA-PANI and acrylamide (AM) was obtained by using N,N′ -methylene-bisacrylamide (MBA) as a cross-linker, and ammonium persulphate/N,N,N′,N′-tetramethylethylenediamine (APS/TMEDA) as an initiating system. The developed materials were characterized by UV–visible, FTIR, XRD, SEM–EDX and TEM techniques. The microscopy studies revealed that GA-PANI nanoparticles have a granular morphological surface with an average size of?~?40–100 nm. Removal of MB dye from aqueous system was performed by adsorption studies in batch equilibrium mode with different dosage of GA-PANI, MB concentration, pH and temperatures. The adsorption data revealed that the absorption capacity of GPA NCHs highly depends on the dosage of GA-PANI, pH and concentration of the MB dye. The maximum percentage of MB removal onto GPA 1.0 NCHs was found to be 89% at pH 10 with a dye concentration of 10 mg L^?1. The equilibrium adsorption data were also analyzed by different models to understand the adsorption process. The results revealed that the adsorption process followed the pseudo-second-order kinetics and it fit well in Langmuir and Freundlich adsorption isotherms with a maximum adsorption capacity of 35.41 mg g^?1. These studies demonstrate that the GPA NCHs could be a promising adsorbent material for the removal of MB dye from contaminated aqueous systems.