Enhanced removal of lead and zinc by a 3D aluminium sulphate-functionalised graphene aerogel as an effective adsorption system.

The discharge of heavy metals into the environment has adversely affected the aquatic ecosystem due to their toxic and non-biodegradable nature. In this research, a three-dimensional graphene oxide/carboxymethylcellulose/aluminium sulphate (GOCAS) aerogel was synthesised and evaluated as a novel means for lead and zinc removal. The GOCAS aerogel was prepared via ice-templating of graphene oxide with carboxymethylcellulose and aluminium sulphate as the crosslinking and functionalisation additives. Characterisation of the aerogel by various analytical techniques confirmed the successful integration of the chemical additives. The hydroxyl and sulphate groups in the aerogel were found to participate in the adsorption of both metals. The equilibrium of lead adsorption was found to correlate well to the Freundlich isotherm, while zinc adsorption fitted closely the Langmuir isotherm. The kinetic adsorption behaviour of both metals was best described as pseudo-second-order. The interactive influences of concentration, temperature, contact time and adsorbent dose on the metal removal were explored by a central composite design, and the optimum adsorption capacity for lead was determined to be 138.7 mg/g at a GOCAS dose of 20 mg, initial concentration of 100 mg/L, temperature of 50 °C and contact time of 45 min. The optimum adsorption capacity for zinc was 52.69 mg/g at 30 mg, 65 mg/L, 45 °C and 40 min. Furthermore, regeneration studies with hydrochloric acid eluant were successfully conducted for up to four adsorption-desorption cycles. Overall, this work demonstrates that GOCAS aerogel is a viable nanosorbent for the adsorption of lead and zinc from water systems.

Evaluation of adsorption performance and mechanisms of a highly effective 3D boron-doped graphene composite for amitriptyline pharmaceutical removal.

Three-dimensional heteroatom-doped graphene presents a state-of-the-art approach for effective remediation of pharmaceutical wastewater on account of its distinguished adsorption and physicochemical attributes. Amitriptyline is an emerging tricyclic antidepressant pollutant posing severe risks to living habitats through water supply and food chain. With ultra-large surface area and plentiful chemical functional groups, graphene oxide is a favorable adsorbent for decontaminating polluted water. Herein, a new boron-doped graphene oxide composite reinforced with carboxymethyl cellulose was successfully developed via solution-based synthesis. Characterization study revealed that the adsorbent was formed by graphene sheets intertwined into a porous network and engrafted with 13.37 at% of boron. The adsorbent has a zero charge at pH 6 and contained various chemical functional groups favoring the attachment of amitriptyline. It was also found that a mere 10 mg of adsorbent was able to achieve relatively high amitriptyline removal (89.31%) at 50 ppm solution concentration and 30 °C. The amitriptyline adsorption attained equilibrium within 60 min across solution concentrations ranging from 10 to 300 ppm. The kinetic and equilibrium of amitriptyline adsorption were well correlated to the pseudo-second-order and Langmuir models, respectively, portraying the highest Langmuir adsorption capacity of 737.4 mg/g. Notably, the predominant mechanism was chemisorption assisted by physisorption that contributed to the outstanding removal of amitriptyline. The saturated adsorbent was sufficiently regenerated using ethanol eluent. The results highlighted the impressive performance of the as-synthesized boron-doped adsorbent in treating amitriptyline-containing waste effluent.

Synthesis of a highly recoverable 3D MnO2/rGO hybrid aerogel for efficient adsorptive separation of pharmaceutical residue.

Water contamination by non-steroidal anti-inflammatory drugs, such as acetaminophen, is an emerging ecological concern. In this study, a new three-dimensional manganese dioxide-engrafted reduced graphene oxide (3D MnO2/rGO) hybrid aerogel was developed for acetaminophen sequestration. The synthesis involved firstly the self-assembly of GO aerogel, followed by thermal reduction and in-situ MnO2 growth by redox-reaction. The aerogel demonstrated interlinked planes with smooth surfaces deposited with MnO2 nanospheres and pores of 138.4 - 235.3 µm width. The influences of adsorbent dosage, initial pH, acetaminophen concentration, temperature and contact time were investigated. It was determined that the adsorption of acetaminophen occurred on uniform sorption sites in the aerogel, as suggested by the best fit of data to the Langmuir isotherm, yielding a maximum adsorption capacity of 252.87 mg/g. This highest adsorption performance of the 3D MnO2/rGO aerogel was attained at a dosage of 0.6 g/L, initial pH of 6.2 and temperature of 40°C. The process kinetics were in-line with the pseudo-first-order and pseudo-second-order kinetics at 10 and 20 - 500 mg/L concentrations, respectively. Thermodynamic assay showed the spontaneity and endothermicity features of the 3D MnO2/rGO-acetaminophen system. The acetaminophen adsorption mechanisms were mainly hydrogen bonding and pore entrapment. Moreover, the as-synthesised aerogel was effectively regenerated using acetone and re-utilised in four adsorption-desorption cycles. Overall, the results highly recommend the implementation of the 3D MnO2/rGO hybrid aerogel for purification of wastewater polluted by acetaminophen residue.

Utilisation of environmentally friendly okara-based biosorbent for cadmium(II) removal.

Heavy metals released by various industries are among the major pollutants found in water resources. In this research, biosorption technique was employed to remove cadmium (Cd2+) from an aqueous system using a novel biosorbent developed from okara waste (OW), a residue from soya bean-based food and beverage processing. Characterisation results revealed that the OW biosorbent contained functional groups such as hydroxyl-, carboxyl- and sulphur-based functional groups, and the surface of the biosorbent was rough with multiple fissures which might be the binding sites for the pollutant. The effects of dosage, solution pH, initial Cd2+ concentration, temperature and contact time were investigated using batch adsorption mode. The biosorption equilibrium and kinetic were best described by the Langmuir and Elovich models, respectively. The maximum biosorption capacities predicted by the Langmuir model were 10.91-14.80 mg/g at 30-70 °C, and the biosorption process was favourable as evident from 0 < RL < 1. The uptake of Cd2+ by the OW biosorbent was spontaneous and endothermic. The plausible biosorption mechanisms of this study could be ionic exchange, hydrogen bonding and electrostatic interactions. The Cd2+ loaded OW biosorbent could be regenerated using 0.4 M of HCl solution and regeneration was studied for 4 adsorption-desorption cycles. The present investigation supported that OW can be reused as a value-added biosorbent product for the removal of Cd2+ from the contaminated water.

Facile synthesis of xanthan biopolymer integrated 3D hierarchical graphene oxide/titanium dioxide composite for adsorptive lead removal in wastewater.

Xanthan integrated graphene oxide functionalized by titanium dioxide was successfully prepared through facile, eco-friendly and cost effective ice-templating technique. The three-dimensional (3D) graphene composite demonstrated relatively high temperature stability, chemical functionalities and porous sponge-like structure. The adsorption of lead was favored by high initial concentration and shaking speed at the operational solution pH. The process equilibrium and kinetic adhered to the Langmuir and pseudo-second-order correlations, respectively. The biomass integrated graphene composite showed maximum adsorption capacities ranging from 132.18 to 199.22 mg/g for 30-70 °C. Moreover, it was highly regenerable under mild conditions (0.1 M hydrochloric acid, 30 °C) and used repeatedly while retaining 84.78% of its initial adsorption capacity at the fifth adsorption-regeneration cycle. With comparatively high lead adsorption capacities, adequate recyclability and environmentally friendliness, the as-prepared 3D graphene composite has high application potential in heavy metal-wastewater separation for protection of the environment and human health.

Environmental application of three-dimensional graphene materials as adsorbents for dyes and heavy metals: Review on ice-templating method and adsorption mechanisms.

The remediation of wastewater requires treatment technologies which are robust, efficient, simple to operate and affordable such as adsorption. Lately, three-dimensional (3D) graphene based materials have attracted significant attention as effective adsorbents for wastewater treatment. The intrinsic properties of 3D graphene structure such as large surface area and interconnected porous structure can facilitate the transport of pollutants into the 3D network and provide abundant active sites for trapping the pollutants. For the synthesis of 3D graphene structure, ice-templating is commonly practiced due to its facile steps, cost effectiveness and high scalability potential. This review covers the ice-templating fabrication technique for 3D graphene based materials and their application as adsorbents in eliminating dyes and heavy metals from aqueous media. The assembly mechanisms of the ice-templating fsynthesis are comprehensively discussed. Further discussion on the fundamental principles, critical process parameters and characteristics of ice-templated 3D graphene structures is also included. A thorough review on the mechanisms for batch adsorption of dyes and heavy metals is presented based on the structures and properties of the 3D graphene materials. The review further evaluates the dynamic adsorption in packed columns and the regeneration of 3D graphene based materials.

Adsorptive decontamination of diclofenac by three-dimensional graphene-based adsorbent: Response surface methodology, adsorption equilibrium, kinetic and thermodynamic studies.

Pharmaceutical residues are emerging pollutants in the aquatic environment and their removal by conventional wastewater treatment methods has proven to be ineffective. This research aimed to develop a three-dimensional reduced graphene oxide aerogel (rGOA) for the removal of diclofenac in aqueous solution. The preparation of rGOA involved facile self-assembly of graphene oxide under a reductive environment of L-ascorbic acid. Characterisation of rGOA was performed by Fourier transform infrared, scanning electron microscope, transmission electron microscopy, nitrogen adsorption-desorption, Raman spectroscopy and X-ray diffraction. The developed rGOA had a measured density of 20.39 ±â€¯5.28 mg/cm3, specific surface area of 132.19 m2/g, cumulative pore volume of 0.5388 cm3/g and point of zero charge of 6.3. A study on the simultaneous interactions of independent factors by response surface methodology suggested dosage and initial concentration as the dominant parameters influencing the adsorption of diclofenac. The highest diclofenac adsorption capacity (596.71 mg/g) was achieved at the optimum conditions of 0.25 g/L dosage, 325 mg/L initial concentration, 200 rpm shaking speed and 30 °C temperature. The adsorption equilibrium data were best fitted to the Freundlich model with correlation coefficient (R2) varying from 0.9500 to 0.9802. The adsorption kinetic data were best correlated to the pseudo-first-order model with R2 ranging from 0.8467 to 0.9621. Thermodynamic analysis showed that the process was spontaneous (∆G = - 7.19 to - 0.48 kJ/mol) and exothermic (∆H = - 12.82 to - 2.17 kJ/mol). This research concluded that rGOA is a very promising adsorbent for the remediation of water polluted by diclofenac.

Ice-templated graphene oxide/chitosan aerogel as an effective adsorbent for sequestration of metanil yellow dye.

Graphene oxide/chitosan aerogel (GOCA) was prepared by a facile ice-templating technique without using any cross-linking reagent for metanil yellow dye sequestration. The adsorption performance of GOCA was investigated by varying the adsorbent mass, shaking speed, initial pH, contact time, concentration and temperature. The combined effects of adsorption parameters and the optimum conditions for dye removal were determined by response surface methodology. GOCA exhibited large removal efficiencies (91.5-96.4%) over a wide pH range (3-8) and a high adsorption capacity of 430.99 mg/g at 8 mg adsorbent mass, 400 mg/L concentration, 35.19 min contact time and 175 rpm shaking speed. The adsorption equilibrium was best represented by the Langmuir model. GOCA could be easily separated after adsorption and regenerated for re-use in 5 adsorption-desorption cycles thereby maintaining 80% of its adsorption capability. The relatively high adsorption and regeneration capabilities of GOCA render it an attractive adsorbent for treatment of azo dye-polluted water.

Assessment of fish scales waste as a low cost and eco-friendly adsorbent for removal of an azo dye: Equilibrium, kinetic and thermodynamic studies.

In this study, AB113 dye was successfully sequestered using a novel adsorbent made of mixed fish scales (MFS). The influence of adsorbent dosage, initial pH, temperature, initial concentration and contact time on the adsorption performance was investigated. The surface chemistry and morphology of the adsorbent were examined by FTIR, TGA and SEM. Amides, phosphate and carbonate groups were evidently responsible for the high affinity of MFS towards the dye. The adsorption equilibrium and kinetic were well described by Langmuir and pseudo-second-order models, respectively. The maximum adsorption capacities of MFS were 145.3-157.3mg/g at 30-50°C. The adsorption of AB113 dye onto the adsorbent was exothermic and spontaneous as reflected by the negative enthalpy and Gibbs energy changes. The results support MFS asa potential adsorbent for AB113 dye removal.

Multistage optimizations of slow pyrolysis synthesis of biochar from palm oil sludge for adsorption of lead.

This research investigated the removal of lead (Pb2+) by a novel biochar derived from palm oil sludge (POS-char) by slow pyrolysis. Multistage optimizations with central composite design were carried out to firstly optimize pyrolysis parameters to produce the best POS-char for Pb2+ removal and secondly to optimize adsorption conditions for the highest removal of Pb2+. The optimum pyrolysis parameters were nitrogen flowrateof30mLmin-1, heating rateof10°Cmin-1, temperatureof500°C and timeof30min. The optimum Pb2+ adsorption conditions were concentrationof200mgL-1, timeof60min, dosageof0.3g and pH of 3.02. The various functional groups within POS-char played a vital role in Pb2+ uptake. Regeneration was demonstrated to be feasible using hydrochloric acid. Adsorption equilibrium was best described by Freundlich model. At low concentration range, adsorption kinetic obeyed pseudo-first-order model, but at high concentration range, it followed pseudo-second-order model. Overall, the results highlighted that POS-char is an effective adsorbent for Pb2+ removal.