Effect of the addition mode of carbon nanotubes for the production of chitosan hydrogel core-shell beads on adsorption of Congo red from aqueous solution

Biopolymer-based beads for the adsorptive removal of organic pollutants from wastewater: Current state and future perspectives

Among biopolymer-based adsorbents, composites in the form of beads have shown promising results in terms of high adsorption capacity and ease of separation from the effluents. This review addresses the potential of biopolymer-based beads to remediate wastewaters polluted with emerging organic contaminants, for instance dyes, active pharmaceutical ingredients, pesticides, phenols, oils, polyaromatic hydrocarbons, and polychlorinated biphenyls. High adsorption capacities up to 2541.76 mg g-1 for dyes, 392 mg g-1 for pesticides and phenols, 1890.3 mg g-1 for pharmaceuticals, and 537 g g-1 for oils and organic solvents have been reported. The review also attempted to convey to its readers the significance of wastewater treatment through adsorption by providing an overview on decontamination technologies of organic water contaminants. Various preparation methods of biopolymer-based gel beads and adsorption mechanisms involved in the process of decontamination have been summarized and analyzed. Therefore, we believe there is an urge to discuss the current state of the application of biopolymer-based gel beads for the adsorption of organic pollutants from wastewater and future perspectives in this regard since it is imperative to treat wastewater before releasing into freshwater bodies.

Nylon fiber waste as a prominent adsorbent for Congo red dye removal

In this research nylon fibers wastes (NF) were fabricated into porous sheet using a phase inversion technique to be utilized as an adsorbent materials for Congo red dye (CR). The fabricated sheet denoted as NS was characterized using FTIR and XRD. The surface studies of the adsorbent materials using SEM and BET analysis reveals a highly pores structure with an average pore volume 0.61 cc/g and BET surface area of 767 m2/g. The adsorption studies of fabricated NS were employed into CR at different parameters as pH, effect of time and dye concentration. The adsorption isotherm and kinetic studies were more fit to Langmuir and pseudo second order models. The maximum adsorption capacity qmax reached 188 mg/g with removal percentage of 95 for CR concentration of 400 mg/L at pH 6 and 0.025 g NS dose for 10 ml CR solution. The regeneration study reveals a prominent adsorption behavior of NS with removal % of 88.6 for CR (300 mg/L) after four adsorption desorption cycles. Effect of incorporation of NaonFil Clay to NS was studied using Response Surface Methodology (RSM) modeling and reveals that 98.4% removal of CR could be achieved by using 19.35% wt. of fiber with 8.2 g/L dose and zero clay, thus at a predetermined parameters studies of NanoFil clay embedded into NS, there are no significant effect for %R for CR.

Progresses in lignin, cellulose, starch, chitosan, chitin, alginate, and gum/carbon nanotube (nano)composites for environmental applications: A review

Water sources are becoming increasingly scarce, and they are contaminated by industrial, residential, and agricultural waste-derived organic and inorganic contaminants. These contaminants may pollute the air, water, and soil in addition to invading the ecosystem. Because carbon nanotubes (CNTs) can undergo surface modification, they can combine with other substances to create nanocomposites (NCs), including biopolymers, metal nanoparticles, proteins, and metal oxides. Furthermore, biopolymers are significant classes of organic materials that are widely used for various applications. They have drawn attention due to their benefits such as environmental friendliness, availability, biocompatibility, safety, etc. As a result, the synthesis of a composite made of CNT and biopolymers can be very effective for a variety of applications, especially those involving the environment. In this review, we reported environmental applications (including removal of dyes, nitro compounds, hazardous materialsو toxic ions, etc.) of composites made of CNT and biopolymers such as lignin, cellulose, starch, chitosan, chitin, alginate, and gum. Also, the effect of different factors such as the medium pH, the pollutant concentration, temperature, and contact time on the adsorption capacity (AC) and the catalytic activity of the composite in the reduction or degradation of various pollutants has been systematically explained.

Amino-functionalized alginate/graphene double-network hydrogel beads for emerging contaminant removal from aqueous solution

Inorganic-organic composite hydrogels have attracted much attention in recent years. In this study, an amino-functionalized graphene/alginate double-network hydrogel (NH₂-DN) with excellent mechanical and adsorption properties was successfully prepared. Triethylenetetramine (TETA) was used as a crosslinker which promotes random few-layer graphene sheets stacking and resulted in a reduced graphene oxide (rGO) network, containing mesopore and macropore structures on the hydrogel surface. Compared to single network hydrogel, enhanced thermal stability and mechanical properties were achieved in NH₂-DN. The elasticity modulus was improved by approximately 3 times due to the formation of the double-network. More importantly, NH₂-DN exhibited excellent adsorption properties for typical emerging contaminants (Cu²⁺ and ciprofloxacin (CIP)). Compared with that of an ordinary graphene/alginate single-network hydrogel (SN), the adsorption capacity of the NH₂-DN for Cu²⁺ and CIP reached 153.91 mg g^-1 and 301.36 mg g^-1, respectively, which was increased by 130% and 182%, respectively. Adsorption isotherm and kinetic analyses reveal that the adsorption process of CIP onto the NH₂-DN was dominated by chemical affinity. Adsorption properties were comprehensively examined, including the effects of the solid-liquid ratios, pH, and ionic strength. NH₂-DN retained 94% of its adsorption capacity when the ionic strength was 0.5 mol L^-1 and maintained at least 87% of its adsorption capacity in weak acidic and alkaline solutions. This novel amino-functionalized organic-inorganic hydrogel has great potential in environmental applications owing to its outstanding physicochemical, mechanical, and adsorption properties for emerging contaminants in wastewater.

Nano-magnetic walnut shell-rice husk for Cd(II) sorption: design and optimization using artificial intelligence and design expert

This study attempted to investigate the use of nanomagnetic activated carbon prepared from walnut shell and rice husk wastes for removal of Cd(II) from aqueous solution via application of ANN and design expert as adsorbent preparation design and optimization tools. The novel adsorbent was characterized using SEM, FTIR, EDS and BET. The result from 2-level factorial design expert revealed 78.58% Cd(II) sorption efficiency could be achieved for adsorbent prepared at optimum calcination temperature, calcination time, SS-RH mixing ratio and magnetite loading of 859.20 °C, 2.32 h, 2.54 and 5.56 wt% respectively. Sensitivity analysis by both proposed methodologies revealed calcination temperature as most influential factor in adsorbent preparation. Average relative errors and R2 values of 1.2931% and 4.806%; and 0.9967 and 0.9055 obtained respectively for developed ANN model with 4-9-1 architecture and 2-level factorial design expert revealed ANN model as better prediction and optimization tool for Cd(II) sorption using NM-WS-RH-AC. Laboratory analysis revealed presence of -OH, -NH and COO- groups on adsorbent surface; presence of Cd(II) after adsorption; change in adsorbent textural and morphological structure after Cd(II) adsorption; and increase in its surface area and average pore diameter due to magnetization. Average relatively stable desorption strength of 62.74% towards Cd(II) was exhibited by adsorbent for four consecutive cycles using 0.1M HNO3. Prepared adsorbent is effective in removing Cd(II) from solution than commercial activated carbon with economically viable regeneration attribute.

Self-Assembled Supramolecular Ribbon-Like Structures Complexed to Single Walled Carbon Nanotubes as Possible Anticancer Drug Delivery Systems

Designing an effective targeted anticancer drug delivery method is still a big challenge, since chemotherapeutics often cause a variety of undesirable side effects affecting normal tissues. This work presents the research on a novel system consisting of single walled carbon nanotubes (SWNT), dispersed with Congo Red (CR), a compound that forms self-assembled ribbon-like structures (SRLS) and anticancer drug doxorubicin (DOX). SWNT provide a large surface for binding of planar aromatic compounds, including drugs, while CR supramolecular ribbon-like assemblies can be intercalated by drugs, like anthracycline rings containing DOX. The mechanism of interactions in SWNT–CR–DOX triple system was proposed based on electrophoretic, spectral, Dynamic Light Scattering and scanning electron microscopy analyzes. The profile of drug release from the investigated system was evaluated using dialysis and Differential Scanning Calorimetry. The results indicate that ribbon-like supramolecular structures of CR bind to SWNT surface forming SWNT–CR complexes which finally bind DOX. The high amount of nanotube-bound CR greatly increases the capacity of the carrier for the drug. The high capacity for drug binding and possible control of its release (through pH changes) in the analyzed system may result in prolonged and localized drug action. The proposed SWNT–CR–DOX triple system meets the basic criteria that justifies its further research as a potential drug carrier.

A review on agro-industrial waste (AIW) derived adsorbents for water and wastewater treatment

There is a large amount of studies surrounding the usage of agro-industrial waste (AIW) for the adsorptions of organic pollutants (dyes) and inorganic pollutants (heavy metals) in water/wastewater. This method is normally treated as an alternative approach to the conventional water/wastewater treatment. However, there are some increasing interests for investigators to identify novel adsorption materials for pollutants removal. It is particularly noteworthy that most AIW wastes are not currently used at the original state, but modified in a variety of ways to reinforce the porosity and adsorption surface area of the material. Nanostructuring, activation, carbonization, and grafting are some common modification technologies of agricultural waste adsorbents. Besides, the characteristic, preparation and application of adsorbents from various industrial wastes, including natural materials and biosorbents, were summarized. Additionally, the challenges and perspectives for future researches of waste-derived adsorbents were studied. This review provides an important insight on using AIWs as precursor materials for preparing adsorbents in water/wastewater treatment.

Synthesis of magnetic functionalized MWCNT nanocomposite through surface RAFT co-polymerization of acrylic acid and N-isopropyl acrylamide for removal of cationic dyes from aqueous solutions

In this study, magnetic multi-walled carbon nanotube (MMWCNT) composites were prepared via surface reversible addition fragmentation chain transfer (RAFT) co-polymerization of acrylic acid (AA) and N-isopropyl acrylamide (NIPAM) in the presence of Fe₃O₄ nanoparticles. First, a novel RAFT agent (RA) was prepared and then immobilized onto the surface of MWCNT to fabricate RA-g-MWCNT. Then, Fe₃O₄ nanoparticles were attached onto the surface of RA-g-MWCNT. Finally, RAFT co-polymerization of AA and NIPAM monomers was carried out via Fe₃O₄-g-RA-g-MWCNT RAFT agent. The structure and morphology of the prepared polymer-coated MWCNT was examined by FTIR, SEM, TEM, XRD, VSM, and TGA. The adsorption behaviours of the cationic dyes were studied. The equilibrium isotherm and kinetics of cationic dyes were investigated. Thermodynamics investigations also depicted that the adsorptions of cationic dyes were spontaneous and endothermic in nature. The synthesized dye adsorbent with high adsorption capacities, reusability, and easy recovery makes it as a good candidate for wastewater treatment.

Facile preparation of water-soluble hyperbranched polyamine functionalized multiwalled carbon nanotubes for high-efficiency organic dye removal from aqueous solution

Water-soluble hyperbranched polyamine functionalized multiwalled carbon nanotubes nanocomposite (WHPA-OMCNT) was successfully prepared and applied to water remediation in this paper. WHPA-OMCNT was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), zeta potential, scanning electron microscopy (SEM) and transmission electron microscope (TEM) analyses. WHPA-OMCNT exhibited excellent adsorption performance for removal of organic dyes e.g., methylene blue (MB), malachite green (MG) and methyl violet (MV). The equilibrium adsorption capacity was 800.0 mg g^-1 for MB, 840.3 mg g^-1 for MG and 970.9 mg g^-1 for MV under the optimal conditions. The pseudo-second order equation and the Langmuir model exhibited good correlation with the adsorption kinetic and isotherm data for all three pollutants, respectively. The thermodynamic results (ΔG < 0, ΔH < 0, ΔS < 0) implied that the adsorption process of MB, MG and MV was feasible, exothermic and spontaneous in nature. A possible adsorption mechanism has been proposed, where H-bonding, electrostatic attraction and π-π stacking interactions dominated the adsorption of the organic dyes. In addition, the excellent reproducibility endowed WHPA-OMCNT with the potential for application in water treatment.

Adsorptive amputation of hazardous azo dye Congo red from wastewater: a critical review

Increasing amount of dyes in an ecosystem has propelled the search of various methods for dye removal. Amongst all the methods, adsorption occupies a prominent place in dye removal. Keeping this in mind, many adsorbents used for the removal of hazardous anionic azo dye Congo red (CR) from aqueous medium were reviewed by the authors. The main objectives behind this review article are to assemble the information on scattered adsorbents and enlighten the wide range of potentially effective adsorbents for CR removal. Thus, CR sorption by various adsorbents such as activated carbon, non-conventional low-cost materials, nanomaterials, composites and nanocomposites are surveyed and critically reviewed as well as their sorption capacities are also compared. This review also explores the grey areas of the adsorption performance of various adsorbents with reference to the effects of pH, contact time, initial dye concentration and adsorbent dosage. The equilibrium adsorption isotherm, kinetic and thermodynamic data of different adsorbents used for CR removal were also analysed. It is evident from a literature survey of more than 290 published papers that nanoparticle and nanocomposite adsorbents have demonstrated outstanding adsorption capabilities for CR. Graphical abstract ᅟ.

Synthesis of imidazolium-crosslinked chitosan aerogel and its prospect as a dye removing adsorbent

Debus–Radziszewski imidazole synthesis was used to obtain crosslinked chitosan aerogel with very high adsorption towards anionic dye.

Shortening and dispersion of single-walled carbon nanotubes upon interaction with mixed supramolecular compounds

Congo red (CR) dye molecules self-associate in water solutions creating ribbon-like supramolecular structures that can bind various aromatic compounds by intercalation, forming mixed supramolecular systems. Mixed supramolecular systems, such as CR-doxorubicin and CR-Evans blue, interact with the surface of carbon nanotubes, leading to their stiffening and ultimately to their breaking and shortening. This work presents a simple method of obtaining short and straight carbon nanotubes with significantly better dispersion in aqueous solutions and consequently improved usability in biological systems.

Novel tunable composites based on bentonite and modified tragacanth gum for removal of acid dyes from aqueous solutions

A series of new adsorbents derived from tragacanth gum-graft-poly(methyl methacrylate) and bentonite (TG-g-PMMA/B) were synthesized.

Aqueous adsorption and removal of organic contaminants by carbon nanotubes

Organic contaminants have become one of the most serious environmental problems, and the removal of organic contaminants (e.g., dyes, pesticides, and pharmaceuticals/drugs) and common industrial organic wastes (e.g., phenols and aromatic amines) from aqueous solutions is of special concern because they are recalcitrant and persistent in the environment. In recent years, carbon nanotubes (CNTs) have been gradually applied to the removal of organic contaminants from wastewater through adsorption processes. This paper reviews recent progress (145 studies published from 2010 to 2013) in the application of CNTs and their composites for the removal of toxic organic pollutants from contaminated water. The paper discusses removal efficiencies and adsorption mechanisms as well as thermodynamics and reaction kinetics. CNTs are predicted to have considerable prospects for wider application to wastewater treatment in the future.

Biomass-derived highly porous functional carbon fabricated by using a free-standing template for efficient removal of methylene blue

Banana peel (BP), a biomass waste, was converted into a valuable highly porous functional carbon material (HPFCM) by a general chelate-assisted co-assembly process. The HPFCMs were fabricated by using Al(III)-based metal-organic framework-like as a free-standing template and commercial Pluronic F127 as a microstructure-directing agent. Several critical variables for fabrication including doses of Al(III) and F127, carbonization temperature had been optimized and the adsorption behavior of HPFCMs was examined by using methylene blue as dye model compound. The optimal adsorbent was validated as HPFCMs-5-1-800, and its equilibrium data were well fitted to the Langmuir isotherm model with a monolayer adsorption capacity of 385.12 mg g(-1) at ambient temperature. The surface physical properties of HPFCMs-5-1-800 were also exemplarily characterized. The findings revealed that the free-standing template is a potential route for preparation of HPFCM from waste BP.

Adsorption of Direct Blue 53 dye from aqueous solutions by multi-walled carbon nanotubes and activated carbon

Multi-walled carbon nanotubes (MWCNT) and powder activated carbon (PAC) were used as adsorbents for adsorption of Direct Blue 53 dye (DB-53) from aqueous solutions. The adsorbents were characterised using Raman spectroscopy, N2 adsorption/desorption isotherms, and scanning and transmission electron microscopy. The effects of initial pH, contact time and temperature on adsorption capacity of the adsorbents were investigated. At pH 2.0, optimum adsorption of the dye was achieved by both adsorbents. Equilibrium contact times of 3 and 4 h were achieved by MWCNT and PAC adsorbents, respectively. The general order kinetic model provided the best fit of the experimental data compared to pseudo-first order and pseudo-second order kinetic adsorption models. For DB-53 dye, the equilibrium data (298-323 K) were best fitted to the Sips isotherm model. The maximum sorption capacity for adsorption of the dye occurred at 323 K, with the values of 409.4 and 135.2 mg g(-1) for MWCNT and PAC, respectively. Studies of adsorption/desorption were conducted and the results showed that DB-53 loaded MWCNT could be regenerated (97.85%) using a mixture 50% acetone + 50% of 3 mol L(-1) NaOH. Simulated dye house effluents were used to evaluate the application of the adsorbents for effluent treatment (removal of 99.87% and 97.00% for MWCNT and PAC, respectively, were recorded).

Effective removal of Congo red dye from aqueous solution using modified xanthan gum/silica hybrid nanocomposite as adsorbent

The aim of this work is to study the feasibility of XG-g-PAM/SiO2 nanocomposite towards its potential application as high performance adsorbent for removal of Congo red (CR) dye from aqueous solution. The surface area, average pore size and total pore volume of the developed nanocomposite has been determined. The efficiency of CR dye adsorption depends on various factors like pH, temperature of the solution, equilibrium time of adsorption, agitation speed, initial concentration of dye and adsorbent dosage. It has been observed that the nanocomposite is having excellent CR dye adsorption capacity (Q0=209.205 mg g(-1)), which is considerably high. The dye adsorption process is controlled by pseudo-second order and intraparticle diffusion kinetic models. The adsorption equilibrium data correlates well with Langmuir isotherm. Desorption study indicates the efficient regeneration ability of the dye loaded nanocomposite.

Adsorptive removal of dyes from aqueous solution onto carbon nanotubes: a review

Adsorption is a widely used technique for the separation and removal of pollutants from wastewaters. Carbon nanotubes (CNTs) are emerging as potential adsorbents because of its well defined cylindrical hollow structure, large surface area, high aspect ratios, hydrophobic wall and easily modified surfaces. In this review, dye adsorption capability of CNTs and CNT based composites from aqueous system has been compiled. This article provides the information about the defect, adsorption sites on CNTs and batch adsorption studies under the influence of various operational parameters such as contact time, solution pH, temperatures etc. and deals with mechanisms involved in adsorption of dyes onto CNTs. From the literature reviewed, it is observed that single walled carbon nanotubes (SWCNTs) show higher adsorption capacity than multi walled carbon nanotubes (MWCNTs) and functionalized and CNT composite have better sorption capacity than as grown CNTs. It is evident from the literature that CNT based nanosorbents have shown good potential for the removal of dyes from aqueous solution. However, still more research work should be focused on the development of cost effective, higher efficient and environmental friendly CNT based nanosorbents for their commercial applications.

Methylene blue adsorption onto swede rape straw (Brassica napus L.) modified by tartaric acid: equilibrium, kinetic and adsorption mechanisms

The aim of this study was to develop a promising and competitive bioadsorbent with the abundant of source, low price and environmentally friendly characters to remove cationic dye from wastewater. The swede rape straw (Brassica napus L.) modified by tartaric acid (SRSTA) was prepared, characterized and used to remove methylene blue (MB) from aqueous solution at varied operational conditions (including MB initial concentrations, adsorbent dose, etc.). Results demonstrated that the equilibrium data was well fitted by Langmuir isotherm model. The maximum MB adsorption capacity of SRSTA was 246.4 mg g(-1), which was comparable to the results of some previous studied activated carbons. The higher dye adsorption capacity could be attributed to the presence of more functional groups such as carboxyl group on the surface of SRSTA. The adsorption mechanism was also discussed. The results indicate that SRSTA is a promising and valuable absorbent to remove methylene blue from wastewater.

Comparison of Spirulina platensis microalgae and commercial activated carbon as adsorbents for the removal of Reactive Red 120 dye from aqueous effluents

Spirulina platensis microalgae (SP) and commercial activated carbon (AC) were compared as adsorbents to remove Reactive Red 120 (RR-120) textile dye from aqueous effluents. The batch adsorption system was evaluated in relation to the initial pH, contact time, initial dye concentration and temperature. An alternative kinetic model (general order kinetic model) was compared with the traditional pseudo-first order and pseudo-second order kinetic models. The equilibrium data were fitted to the Langmuir, Freundlich and Liu isotherm models, and the thermodynamic parameters were also estimated. Finally, the adsorbents were employed to treat a simulated dye-house effluent. The general order kinetic model was more appropriate to explain RR-120 adsorption by SP and AC. The equilibrium data were best fitted to the Liu isotherm model. The maximum adsorption capacities of RR-120 dye were found at pH 2 and 298 K, and the values were 482.2 and 267.2 mg g(-1) for the SP and AC adsorbents, respectively. The thermodynamic study showed that the adsorption was exothermic, spontaneous and favourable. The SP and AC adsorbents presented good performance for the treatment of simulated industrial textile effluents, removing 94.4-99.0% and 93.6-97.7%, respectively, of the dye mixtures containing high saline concentrations.

Adsorption of Reactive Red M-2BE dye from water solutions by multi-walled carbon nanotubes and activated carbon

Multi-walled carbon nanotubes and powdered activated carbon were used as adsorbents for the successful removal of Reactive Red M-2BE textile dye from aqueous solutions. The adsorbents were characterised by infrared spectroscopy, N(2) adsorption/desorption isotherms and scanning electron microscopy. The effects of pH, shaking time and temperature on adsorption capacity were studied. In the acidic pH region (pH 2.0), the adsorption of the dye was favourable using both adsorbents. The contact time to obtain equilibrium at 298K was fixed at 1h for both adsorbents. The activation energy of the adsorption process was evaluated from 298 to 323K for both adsorbents. The Avrami fractional-order kinetic model provided the best fit to the experimental data compared with pseudo-first-order or pseudo-second-order kinetic adsorption models. For Reactive Red M-2BE dye, the equilibrium data were best fitted to the Liu isotherm model. Simulated dyehouse effluents were used to check the applicability of the proposed adsorbents for effluent treatment.