A review on applicability of naturally available adsorbents for the removal of hazardous dyes from aqueous waste

Superhydrophilic PANI/Ag/TA@PVDF Composite Membrane with Antifouling Property for Oil-Water Separation

The current membrane materials used for oil-water separation suffer from low separation efficiency and poor durability, and membrane contamination is also a key issue that must be addressed urgently. In this paper, a superhydrophilic PANI/Ag/TA@PVDF composite membrane with PANI-Ag NPs heterojunction structure was prepared via chelation and reduction of Ag+ by tannic acid (TA) and in situ growth of hydrochloric acid-doped polyaniline (PANI). TA endows the prepared composite membrane with excellent superhydrophilicity and underwater oleophobicity, remarkable oil-water separation capacity (the separation efficiency of more than 97% for soybean oil), and extraordinary antifouling properties. Notably, the range of photodegradation is expanded from UV to visible light by the construction of a Schottky heterostructure between PANI and Ag NPs, the photocatalytic degradation ability of composite membrane for organic pollutants has been improved obviously, and the degradation efficiency for crystal violet (CV) is 97.9%. Considering these merits, the PANI/Ag/TA@PVDF composite membrane provides an effective strategy to overcome the shortcomings of existing membrane materials, presenting enormous potential in the treatment and purification of oily wastewater.

Controversial Issues Related to Dye Adsorption on Clay Minerals: A Critical Review

This critical review points out the most serious and problematic issues to be found in the literature on the adsorption of dyes on clay minerals. The introduction draws attention to the fundamental problems, namely the insufficient characterization of adsorbents, the influence of impurities on the adsorption of dyes, and the choice of inappropriate models for the description of the very complex systems that clay minerals and their systems represent. This paper discusses the main processes accompanying adsorption in colloidal systems of clay minerals. The relationship between the stability of the colloidal systems and the adsorption of dye molecules is analyzed. The usual methodological procedures for determining and evaluating the adsorption of dyes are critically reviewed. A brief overview and examples of modified clay minerals and complex systems for the adsorption of organic dyes are summarized. This review is a guide for avoiding some faults in characterizing the adsorption of organic dyes on clay minerals, to improve the procedure for determining adsorption, to evaluate results correctly, and to find an appropriate theoretical interpretation. The main message of this article is a critical analysis of the current state of the research in this field, but at the same time, it is a guide on how to avoid the most common problems and mistakes.

Preparation of cellulose gel extracted from rice straw and its application for metal ion removal from aqueous solutions

Rice straw waste was used to extract natural cellulose fibers, which was then chemically converted to cellulose gel. Both extracted cellulose and modified cellulose (gel) were characterized using different techniques and used for biosorption of b+arium, manganese, cobalt, nickel, copper, zinc, and cadmium. Both celluloses' chemical compositions were investigated. The FT-IR, XRD, TEM, and SEM results all support the success of the proposed chemical modification. Because of the increase in pore size within the gel composition, the metal sorption capability of the final chelating material (gel) was greater than that of extracted cellulose. The experimental data were fit to the sorption isotherm models of Langmuir, Freundlich, and Temkin. This new modified biopolymer's behaviour suggested that it could be used as a promising sorbent for cation removal from polluted dye baths and waste water. Furthermore, this modified cellulose was prepared as cheap material extracted from the rise waste which helping in protection of the environment and it was confirm excellent behaviour in the removal heavy metals from their aqueous solution compared to the previous materials reported before.

Synthesis of a novel porous organic polymer containing triazine and cyclohexanone rings as an efficient methyl red adsorbent from aqueous solutions

In this research, a new porous organic polymer based on triazine and cyclohexanone rings was synthesized via Schiff base condensation, and its performance as an adsorbent for the removal of Methyl Red dye from aqueous solution was investigated. The synthesized polymer was characterized by FT-IR, XRD, SEM, EDS, TEM, TGA, and BET analyses. Five important parameters of pH (4-10), contact time (10-120 min), adsorbent dose (5-10 mg), initial dye concentration (10-70 mg/L), and temperature (25-45 °C) were investigated to optimize the adsorption conditions. Solution pH of 4, contact time of 80 min, adsorbent dose of 8 mg, initial dye concentration of 50 mg/L, and temperature of 45 °C were obtained as the best conditions for the adsorption of methyl red dye. Two widely used Langmuir and Freundlich models were employed to investigate the adsorption isotherm, and the obtained data showed that the adsorption process follows the Langmuir isotherm with a correlation coefficient (R2 = 0.9784) which indicates monolayer adsorption. The achieved maximum adsorption capacity was 178.57 mg/g. Also, the results of kinetic studies indicate that the adsorption process follows the pseudo-second-order kinetic, which suggests that chemical interactions play an important role in dye removal. Furthermore, the results showed that the adsorption process of methyl red dye by polymer is endothermic.

Production of Activated Carbon from Sifted Coke and Determination of Its Physicochemical Characteristics

The possibility of obtaining effective coal sorbents from a low-liquid product of coke chemical production-coke fines-has been studied. To obtain a coal sorbent, coke fines with a size of ≤10 mm were crushed and sieved to obtain a fraction of 2-5 mm. The resulting fraction was activated in a specially designed reactor at 850 °C with steam treatment. Activation was carried out at different durations of the process: 60, 90, and 120 min. It was found that the sample obtained with a process duration of 120 min has the best indicator for the ability to remove phenol from aqueous solutions (74.94 mg/g) and methylene blue (145 mg/g). When cleaning tap water with the resulting carbon sorbent, there is a decrease in the content of calcium, sulfates, and bicarbonate and a decrease in total mineralization. Obtained activated carbon was studied by scanning electron microscopy, low-temperature nitrogen adsorption (BET), and FTIR spectroscopy. It was found that the resulting activated carbon has a porous structure consisting of meso- and macropores, and the specific surface value was ~301 m2/g. The presence of high-intensity absorption bands corresponding to acid functional groups has also been established.

Effective assessment of biopolymer-based multifunctional sorbents for the remediation of environmentally hazardous contaminants from aqueous solutions

Persistent contaminants in wastewater effluent pose a significant threat to aquatic life and are one of the most significant environmental concerns of our time. Although there are a variety of traditional methods available in wastewater treatment, including adsorption, coagulation, flocculation, ion exchange, membrane filtration, co-precipitation and solvent extraction, none of these have been found to be significantly cost-effective in removing toxic pollutants from the water environment. The upfront costs of these treatment methods are extremely high, and they require the use of harmful synthetic chemicals. For this reason, the development of new technologies for the treatment and recycling of wastewater is an absolute necessity. Our way of life can be made more sustainable by the synthesis of adsorbents based on biomass, making the process less harmful to the environment. Biopolymers offer a sustainable alternative to synthetic polymers, which are manufactured by joining monomer units through covalent bonding. This review presents a detailed classification of biopolymers such as pectin, alginate, chitosan, lignin, cellulose, chitin, carrageen, certain proteins, and other microbial biomass compounds and composites, with a focus on their sources, methods of synthesis, and prospective applications in wastewater treatment. A concise summary of the extensive body of knowledge on the fate of biopolymers after adsorption is also provided. Finally, consideration is given to open questions about future developments leading to environmentally friendly and economically beneficial applications of biopolymers.

Photosensitive Dye as an Ideal Peroxymonosulfate Activator for Efficient Self-Degradation: A Novel Idea of Using Waste to Treat Waste

Commonly used peroxydisulfate (PS) or peroxymonosulfate (PMS) activation methods have been limited in their practical application due to certain drawbacks, such as high cost, high energy consumption and secondary pollution. In this study, a catalyst-free alizarin green (AG) self-activating PMS catalytic system was constructed based on photosensitization properties of dye, which ultimately achieved efficient degradation of the dye activator, also the target pollutant. Here, 52.5% of the 100 mL mixture of 10 mg/L AG decomposed within 60 min with 1 mM PMS under visible-light irradiation, thereby showing a strong pH adaptation. Mechanism of AG self-activating PMS was revealed that the photo-excited AG can effectively transfer photo-induced electrons to PMS for its activation, which generates reactive oxidizing species dominated by singlet oxygen (¹O₂), and supplemented by hydroxyl radical (•OH), superoxide radical (O₂^•-) and sulfate radical (SO₄^•-) to realize the efficient self-degradation of the dye pollutants. Moreover, such self-catalytic system operated well under natural sunlight irradiation, indicating the great application potential in the actual wastewater treatment. Herein, photosensitive dye acted as an ideal PMS activator realizing its efficient self-degradation, which provides a novel idea of "using waste to treat waste" for developing wastewater treatment process in a high-efficiency and low-consumption way.

Cadmium and lead ions adsorption on magnetite, silica, alumina, and cellulosic materials

The adsorption of small particles on the surface of an adsorbent depends on interfacial dynamics and associated parameters, including the adsorbate reactivity, adsorbent surface activity, and matrix porosity and tortuosity. Herein, the effect of the surfaces of magnetite, silica/alumina, and silica-cellulose matrix on cadmium adsorption is termed using spectroscopic methods. Atomic absorption spectroscopy was used to determine the adsorption of metal ions in the solid-liquid interfaces by the batch method with different pH, metal concentrations, and contact times. Cadmium (II) were well adsorbed on the magnetite-inorganic surface (around 90% adsorption) rather than other types of semi-organic surfaces, silica, silica-alumina and other cellulosic materials (less than 60% adsorption for Cadmium (II) and 80% of Lead (II) ions). The presence of lead (II) changed the cadmium adsorption behaviour, indicating that adsorption-desorption was a physical interaction on different surfaces. Most absorptions are pH-dependent, stable for Cadmium ions and vary for Lead ions. Moreover, the adsorption analysis using Langmuir and Freundlich isotherms showed no significant characteristics of chemical interaction of the ions with the surfaces as indicated by low R2 values (both around 0.5) for magnetite materials higher for cellulose materials of Langmuir and Freundlich isotherms. This study is beneficial for various fields, such as material science and environmental chemistry, which will play an essential role in the future.

Chemical modification of microcrystalline cellulose with polyethyleneimine and hydrazine: Characterization and evaluation of its adsorption power toward anionic dyes

Functionalization and various applications of biomaterials have progressively gained a major interest due to the cost-effectiveness, renewability, and biodegradability of these substrates. The current work focalized on the functionalization of microcrystalline cellulose with polyethyleneimine solution (3 %, 5 %, and 10 %) and hydrazine sulfate salt (1:1, 1:2, 2:1) using an impregnation method. Untreated and treated samples were characterized using FT-IR, SEM, XRD, TGA, and DTA analyses. The crystallinity index values for control microcrystalline cellulose, cellulose-polyethyleneimine, and cellulose-hydrazine were 57.13.8 %, 57.29 %, and 52.62 %, respectively. Cellulose-polyethyleneimine (5 %) and cellulose-hydrazine (1:1) displayed the highest adsorption capacities for calmagite (an anionic dye). At equilibrium, the maximum adsorption capacities for calmagite achieved 104 mg/g for cellulose-polyethyleneimine (5 %), 45 mg/g for cellulose-hydrazine (1:1), and only 12.4 mg/g for untreated cellulose. Adsorption kinetics complied well with the pseudo-second-order kinetic model. The adsorption isotherm fitted well with the Langmuir isotherm. Overall, the functionalized cellulosic samples could be considered potential materials for the treatment of contaminated waters.

WITHDRAWN: Heavy metal ions and dyes removal from aqueous solution using Aloevera-based biosorbent: A systematic review

This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been withdrawn at the request of the authors, editor and publisher. The publisher regrets that an error occurred which led to the premature publication of this paper. The publisher apologizes to the readers for this unfortunate erro

Appealing Renewable Materials in Green Chemistry

In just a few years, chemists have significantly changed their approach to the synthesis of organic molecules in the laboratory and industry. Researchers are encouraged to approach "greener" reagents, solvents, and methodologies, to go hand in hand with the world's environmental matter, such as water, soil, and air pollution. The employment of plant and animal derivates that are commonly regarded as "waste material" has paved the way for the development of new green strategies. In this review, the most important innovations in this field have been highlighted, paying due attention to those materials that have played a crucial role in organic reactions: wool, silk, and feather. Moreover, we decided to focus on the other most important supports and catalysts in green syntheses, such as proteins and their derivates. Different materials have shown prominent activity in the adsorption of metals and organic dyes, which has constituted a relevant scope in the last two decades. We intend to furnish a complete screening of the application given to these materials and contribute to their potential future utilization.

Sewage sludge-derived biochar for the adsorptive removal of wastewater pollutants: A critical review

The production of biochar from sewage sludge pyrolysis is a promising approach to transform the waste resultant from wastewater treatment plants (WWTPs) to a potential adsorbent. The current review provides an up-to-date review regarding important aspects of sewage sludge pyrolysis, highlighting the process that results major solid fraction (biochar), as high-value product. Further, the physio-chemical characteristics of sewage-sludge derived biochar such as the elemental composition, specific surface area, pore size and volume, the functional groups, surface morphology and heavy metal content are discussed. Recent progress on adsorption of metals, emerging pollutants, dyes, nutrients and oil are discussed and the results are examined. The sewage sludge-derived biochar is a promising material that can make significant contributions on pollutants removal from water by adsorption and additional benefit of the management of huge volume of sewage. Considering all these aspects, this field of research still needs more attention from the researchers in the direction of the technological features and sustainability aspects.

Applications of chitin and chitosan based biomaterials for the adsorptive removal of textile dyes from water - A comprehensive review

The presence of pollutants in the water bodies deteriorate the water quality and make it unfit for use. From an environmental perspective, it is essential to develop new technologies for the wastewater treatment and recycling of dye contaminated water. The surface modified chitin and chitosan biopolymeric composites based adsorbents, have an important role in the toxic organic dyes from removal wastewater. The surface modification of biopolymers with various organics and inorganics produces more active sites at the surface of the adsorbent, which enhances dye and adsorbent interaction more reliable. Herein, the work brought in the thought of the application of various chitin and chitosan composites in wastewater remediation and suggested the versatility in composites for the development of rapid, selective and effective removal processes for the detoxification of a variety of organic dyes. It further emphasizes the existing obstruction and impending prediction for the deprivation of dyes via adsorption techniques.

Critical review on hazardous pollutants in water environment: Occurrence, monitoring, fate, removal technologies and risk assessment

Water is required for the existence of all living things. Water pollution has grown significantly, over the decades and now it has developed as a serious worldwide problem. The presence and persistence of Hazardous pollutants such as dyes, pharmaceuticals and personal care products, heavy metals, fertilizer and pesticides and their transformed products are the matter of serious environmental and health concerns. A variety of approaches have been tried to clean up water and maintain water quality. The type of pollutants present in the water determines the bulk of technological solutions. The main objective of this article was to review the occurrences and fate of hazardous contaminants (dyes, pharmaceuticals and personal care products, heavy metals, and pesticides) found in wastewater effluents. These effluents mingle with other streams of water and that are utilized for a variety of reasons such as irrigation and other domestic activities that is further complicating the issue. It also discussed traditional treatment approaches as well as current advances in hazardous pollutants removal employing graphite oxides, carbon nanotubes, metal organic structures, magnetic nano composites, and other innovative forms of useable materials. It also discussed the identification and quantification of harmful pollutants using various approaches, as well as current advancements. Finally, a risk assessment of hazardous pollutants in water is provided in terms of the human health and the environment. This data is anticipated to serve as a foundation for future improvements in hazardous pollutant risk assessment. Furthermore, future studies on hazardous pollutants must not only emphasize on the parent chemicals, as well as on their possible breakdown products in various media.

Development of a continuous fixed-bed column to eliminate cadmium(II) ions by starch-g-poly(acrylic acid)/cellulose nanofiber bio-nanocomposite hydrogel

This paper presents an experimental study on continuous adsorptive removal of Cd²⁺ from the water body using a bio-nanocomposite hydrogel within a fixed-bed column (FBC) system. The bio-nanocomposite hydrogel was synthesized based on starch grafted poly(acrylic acid) (St-g-PAA) reinforced by cellulose nanofibers (CNFs). The effects of processing conditions including pH, flow rate, and initial concentration of Cd²⁺ on adsorption efficiency were examined. Based on the results, the highest removal efficiency was achieved to be 82.5% at pH of 5, initial concentration of 10 mg L^-1, and flow rate of 5 mL min^-1. Furthermore, by applying isotherm models, it was uncovered that the Langmuir isotherm model was the most appropriate one, and the maximum adsorption capacity was 40.65 mg g^-1. Also, an adsorption process was carried out using the FBC system, and the outcome data were processed using Thomas and Yoon-Nelson models to find the characteristics of the column. In this study, the recovering capacity of the exhausted hydrogel was evaluated. Desorption process efficiencies of batch and continuous operations were obtained to be 91.9% and 90%, respectively.

Application of adsorption process for effective removal of emerging contaminants from water and wastewater

Emerging pollutants in the marine ecosystem, as well as their possible impact on live species, have become a rising cause of worry. A traditional wastewater treatment plants alone are not successful in eliminating such massive contaminant groups and therefore additional water treatment is required which is to be cost effective. Since standard primary and secondary treatment plants are unsuccessful at eliminating or degrading these harmful chemicals, a cost-effective tertiary treatment approach is proposed. Adsorption is a successful approach for Contaminants removal globally, because it is low installation expense, high performance and has easy operational design. Emerging pollutants have been removed from wastewaters using various adsorbents like activated carbons, improved bio chars, Nano adsorbents, hybrid adsorbents, and others. The purpose of this paper is to review the source of contaminants and the concept of adsorption when separating emerging contaminants. The present study aims to examine the adsorption mechanism as an effective approach for treating emerging contaminants. Then, the analysis of natural and man-made adsorbents for the separation of contaminants is examined along with its comparison. Also, future view on emerging contaminants and adsorbents in modern generation has been discussed.

Aloe vera as Promising Material for Water Treatment: A Review

Aloe vera plant offers a sustainable solution for the removal of various pollutants from water. Due to its chemical composition, Aloe vera has been explored as coagulant/flocculant and biosorbent for water treatment. Most of the used materials displayed significant pollutants removals depending on the used preparation methods. AV-based materials have been investigated and successfully used as coagulant/flocculant for water treatment at laboratory scale. Selected AV-based materials could reduce the solids (total suspended solids (TSS), suspended solids (SS), total dissolved solids (TDS), and dissolved solids (DS)), turbidity, chemical oxygen demand (COD), biochemical oxygen demand (BOD), heavy metals, and color, with removal percentages varied depending on the coagulant/flocculant materials and on the wastewater characteristics. In the same context, AV materials can be used as biological flocculant for wastewater sludge treatment, allowing good solid–liquid separation and promoting sludge settling. Moreover, using different methods, AV material-based biosorbents were prepared and successfully used for pollutants (heavy metal dyes and phenol) elimination from water. Related results showed significant pollutant removal efficiency associated with an interesting adsorption capacity comparable to other biosorbents derived from natural products. Interestingly, the enzymatic system of Aloe vera (carboxypeptidase, glutathione peroxidase, and superoxide dismutase) has been exploited to degrade textile dyes. The obtained results showed high promise for removal efficiencies of various kinds of pollutants. However, results varied depending on the methodology used to prepare the Aloe vera based materials. Because of its valuable properties (composition, abundance, ecofriendly and biodegradable), Aloe vera may be useful for water treatment.

Kinetics and thermodynamic studies of Methyl Orange removal by polyvinylidene fluoride-PEDOT mats

We report the preparation of poly(3,4-ethylene dioxythiophene) (PEDOT)-modified polyvinylidene fluoride electrospun fibers and their use as a novel adsorbent material for the removal of the anionic dye Methyl Orange (MO) from aqueous media. This novel adsorbent material can be used to selectively remove MO on a wide pH range (3.0-10.0), with a maximum capacity of 143.8 mg/g at pH 3.0. When used in a recirculating filtration system, the maximum absorption capacity was reached in a shorter time (20 min) than that observed for batch mode experiments (360 min). Based on the analyses of the kinetics and adsorption isotherm data, one can conclude that the predominant mechanism of interaction between the membrane and the dissolved dye molecules is electrostatic. Besides, considering the estimated values for the Gibbs energy, and entropy and enthalpy changes, it was established that the adsorption process is spontaneous and occurs in an endothermic manner. The good mechanical and environmental stability of these membranes allowed their use in at least 20 consecutive adsorption/desorption cycles, without significant loss of their characteristics. We suggest that the physical-chemical characteristics of PEDOT make these hybrid mats a promising adsorbent material for use in water remediation protocols and effluent treatment systems.

Adsorption and biodegradation removal of methylene blue in a down-flow hanging filter reactor incorporating natural adsorbent

This study was carried out to explore the importance of adsorption and biodegradation mechanisms for methylene blue (MB) removal by a novel natural adsorbent (purified coconut fibre; PCF) incorporated to a down-flow hanging fibre (DHF) reactor. An adsorption DHF (Ads-DHF) reactor demonstrated the adsorption removal mechanism, while a combined adsorption-biological DHF (Bio-DHF) reactor simulated the processes of both adsorption and biodegradation were investigated for the MB removal capability. PCF prepared from coconut fibre waste was applied as a media in the DHF reactors. The process performance and the removal mechanisms of the DHF reactors were evaluated for 62 days. The results showed that a total MB removal efficiency of 93 ± 7% was achieved for the Bio-DHF reactor and 36 ± 25% for the Ads-DHF reactor. The combined adsorption and biological degradation in the Bio-DHF reactor enhanced the removal efficiency and the life-time of the reactor compared with the performance of the adsorption process alone in the Ads-DHF reactor. Moreover, microbial community analysis revealed that microorganisms, commonly involved in the biodegradation of dyes, were predominant in the Bio-DHF reactor. The PCF media of the Bio-DHF reactor was essential to keep the dye degrading bacteria in the reactor. Therefore, it can be concluded that the Bio-DHF reactor is an appropriate treatment system for treating dyes wastewater. This research is significant and useful for environmental protection and reuse of biomass wastes.

Microcrystalline Cellulose from Groundnut Shell as Potential Adsorbent of Crystal Violet and Methylene Blue. Kinetics, Isotherms and Thermodynamic Studies

The isolation of microcrystalline cellulose from a groundnut shell is reported. Adsorption experiments were carried out for the removal of cationic crystal violet and methylene blue and it follows Langmuir model. Positive enthalpy and negative free energy changes have shown endothermic and favorable processes. The results reflect good adsorption process.

Inexpensive Organic Materials and Their Applications towards Heavy Metal Attenuation in Waters from Southern Peru

There is interest in using locally available, low cost organic materials to attenuate heavy metals such as Cd, Cr, Cu, Hg, Ni, Pb, and Zn found in surface waters in Peru and other developing regions. Here we mesh Spanish language publications, archived theses, and prior globally available literature to provide a tabulated synthesis of organic materials that hold promise for this application in the developing world. In total, nearly 200 materials were grouped into source categories such as algae and seashells, bacteria and fungi, terrestrial plant-derived materials, and other agricultural and processing materials. This curation was complemented by an assessment of removal potential that can serve as a resource for future studies. We also identified a subset of Peruvian materials that hold particular promise for further investigation, including seashell-based mixed media, fungal blends, lignocellulose-based substrates including sawdust, corn and rice husks, and food residuals including peels from potatoes and avocadoes. Many studies reported percent removal and/or lacked consistent protocols for solid to liquid ratios and defined aqueous concentrations, which limits direct application. However, they hold value as an initial screening methodology informed by local knowledge and insights that could enable adoption for agriculture and other non-potable water reuse applications. While underlying removal mechanisms were presumed to rely on sorptive processes, this should be confirmed in promising materials with subsequent experimentation to quantify active sites and capacities by generating sorption isotherms with a focus on environmental conditions and specific contaminated water properties (pH, temperature, ionic strength, etc.). These organics also hold promise for the pairing of sorption to indirect microbial respiratory processes such as biogenic sulfide complexation. Conversely, there is a need to quantify unwanted contaminant release that could include soluble organic matter and nutrients. In addition to local availability and treatment efficacy, social, technical, economic, and environmental applicability of those materials for large-scale application must be considered to further refine material selection.

Hybrid Aerogel Nanocomposite of Dendritic Colloidal Silica and Hairy Nanocellulose: an Effective Dye Adsorbent

In this study, a new type of silica-cellulose hybrid aerogel was synthesized through a green and facile chemical cross-linking process. In a first step, dendritic fibrous nanostructured (colloidal) silica particles (DFNS) were prepared by a simple hydrothermal technique. Then, the surface of DFNS particles was functionalized with amine groups using 3-aminopropyltriethoxysilane to produce DFNS-NH₂. In a second step, bifunctional hairy nanocellulose (BHNC) particles were functionalized with both aldehyde and carboxylic groups. The aldehyde groups of BHNC and the amine groups of DFNS-NH₂ chemically reacted through a Schiff base reaction to form a hybrid hydrogel nanocomposite. Therefore, no external cross-linker is required in the synthesis. This hybrid aerogel is very lightweight and highly porous with a density of 0.107 g mL^-1 and a porosity of 93.0 ± 0.4%. It has a large surface area of 350 m² g^-1, a large pore volume of 0.23 cm³ g^-1, and a small pore size of 3.9 nm. The developed aerogel contains both positively and negatively charged functional groups and is a highly efficient substrate for dye adsorption from water, for both cationic and anionic organic dyes. These aerogels were found to have an outstanding adsorption capacity toward methylene blue (MB) as a cationic dye and methyl orange (MO) as an anionic dye. The results show that the aerogels can adsorb MB and MO with a capacity of 270 and 300 mg dye/g adsorbent, respectively.

Myco-decontamination of azo dyes: nano-augmentation technologies

Effluents of textile, paper, and related industries contain significant amounts of synthetic dyes which has serious environmental and health implications. Remediation of dyes through physical and chemical techniques has specific limitations. Augmented biological decontamination strategies 'microbial remediation' may involve ring-opening of dye molecules besides the reduction of constituent metal ions. Both bacterial and fungal genera are known to exhibit metabolic versatility which can be harnessed for effective bio-removal of the toxic dye contaminants. Ascomycetous/basidiomycetes fungi can effectively decontaminate azo dyes through laccase/peroxidase enzyme-mediated catalysis. The extent, efficacy, and range of fungal dye decontamination can be enhanced by the conjugated application of nanomaterials, including nanoparticles (NPs) and their composites. Fungal cell-enabled NP synthesis- 'myco-farmed NPs', is a low-cost strategy for scaled-up fabrication of a variety of metal, metal oxide, non-metal oxide NPs through oxidation/reduction of dissolved ions/molecules by extracellular biomolecules. Augmented and rapid decontamination of azo dyes at high concentrations can be achieved by the use of myco-farmed NPs, NPs adsorbed fungal biomass, and nano-immobilized fungi-derived bio-catalytical agents. This manuscript will explore the opportunities and benefits of mycoremediation and application of fungus-NP bionanoconjugate to remediate dye pollutants in wastewaters and land contaminated with the effluent of textile industries.

Magnetic Porous Controlled Fe3O4-Chitosan Nanostructure: An Ecofriendly Adsorbent for Efficient Removal of Azo Dyes

In this work, chitosan/magnetite nanoparticles (ChM) were quickly synthesized according to our previous report based on co-precipitation reaction under ultrasound (US) irradiation. Besides ChM was in-depth structurally characterized, showing a crystalline phase corresponding to magnetite and presenting a spheric morphology, a "nanorod"-type morphology was also obtained after increasing reaction time for eight minutes. Successfully, both morphologies presented a nanoscale range with an average particle size of approximately 5-30 nm, providing a superparamagnetic behavior with saturation magnetization ranging from 44 to 57 emu·g^-1. As ChM nanocomposites have shown great versatility considering their properties, we proposed a comparative study using three different amine-based nanoparticles, non-surface-modified and surface-modified, for removal of azo dyes from aqueous solutions. From nitrogen adsorption-desorption isotherm results, the surface-modified ChMs increased the specific surface area and pore size. Additionally, the adsorption of anionic azo dyes (reactive black 5 (RB5) and methyl orange (MO)) on nanocomposites surface was pH-dependent, where surface-modified samples presented a better response under pH 4 and non-modified one under pH 8. Indeed, adsorption capacity results also showed different adsorption mechanisms, molecular size effect and electrostatic attraction, for unmodified and modified ChMs, respectively. Herein, considering all results and nanocomposite-type structure, ChM nanoparticles seem to be a suitable potential alternative for conventional anionic dyes adsorbents, as well as both primary materials source, chitosan and magnetite, are costless and easily supplied.

Improved Dye Removal Ability of Modified Rice Husk with Effluent from Alkaline Scouring Based on the Circular Economy Concept

To improve the ability of the rice husk to purify colored wastewater, effluent from the alkaline scouring of cotton yarn was used immediately after the scouring (without cooling and additionally added chemicals) in order to remove the non-cellulosic silicon-lignin shield from the rice husk’s surface. This rice husk, with 93.8 mg/g adsorption capacity, behaves similarly as the rice husk treated with an optimized alkaline scouring recipe consisting of 20 g/L NaOH, 2 mL/L Cotoblanc HTD-N and 1 mL/L Kemonecer NI at 70 °C for 30 min with an adsorption capacity of 88.9 mg/g of direct Congo red dye. Treating one form of waste (rice husk) with another (effluent from the alkaline scouring of cellulosic plant fibers), in an effort to produce a material able to purify colored effluent, is an elegant environment-friendly concept based on the circular economy strategy. This will result in a closed-loop energy-efficient process of the pre-treatment of cotton (alkaline scouring), modification of rice husk using effluent from the alkaline scouring, dyeing cotton fabrics and cleaning its colored effluents with modified rice husk without adding chemicals and energy for heating.

Nascent Rice Husk as an Adsorbent for Removing Cationic Dyes from Textile Wastewater

We assessed the applicability of rice husk (RH) to remove cationic dyes, i.e., methylene blue (MB) and crystal violet (CV), from water. RH thermally treated at 75 °C showed a higher adsorption capacity than that at high temperatures (300–700 °C). For a suitable CV-adsorption model, a pseudo-first-order model for MB adsorption was followed by the kinetics adsorption process; however, a pseudo-second-order model was then suggested. In the qt versus t1/2 plot, the MB line passed through the origin, but that of CV did not. The Langmuir isotherm model was better than the Freundlich model for both dye adsorptions; furthermore, the adsorption capacity for MB and CV was 24.48 mg/g and 25.46 mg/g, respectively. Thermodynamically, the adsorption of both MB and CV onto the RH was found to be spontaneous and endothermic. This adsorption increased insignificantly on increasing the solution pH from 4 to 10. With an increasing dosage of the RH, there was an increase in the removal percentages of MB and CV; however, adsorption capacity per unit mass of the RH was observed to decrease. Therefore, we conclude that utilizing RH as an available and affordable adsorbent is feasible to remove MB and CV from wastewater.

Utilization of Composts for Adsorption of Methylene Blue from Aqueous Solutions: Kinetics and Equilibrium Studies

Utilization of composts as low-cost adsorbents is an important application in the field of environmental remediation, but these materials have not yet been extensively used for dye removal. In this work, we have studied the characteristics of adsorption of methylene blue onto two composts (a municipal solid waste compost and a pine bark compost). Kinetics and equilibrium batch experiments testing the influence of adsorbent particle size, solution pH and ionic strength were performed. Both composts have a high adsorption capacity for methylene blue, similar to other low-cost adsorbents. Kinetics of adsorption followed a pseudo-first-order model, with maximum adsorption reached after a contact time of two hours. Equilibrium adsorption followed a Langmuir model in general. Reduction of particle size only increased adsorption slightly for composted pine bark. Increase in ionic strength had no effect on adsorption by municipal solid waste compost, but increased adsorption by composted pine bark. Modification of pH between 5 and 7 did not influence adsorption in any case. Overall, the results suggest that electrostatic interaction between the cationic dye and the anionic functional groups in the composts is not the only mechanism involved in adsorption. In conclusion, the use of composts for dye removal is a likely application, in particular for those composts presenting limitations for agricultural use.

Adsorption of colour from dye wastewater effluent of a down-flow hanging sponge reactor on purified coconut fibre

This study was carried out to evaluate the potential application of agricultural waste coconut (Cocos nucifera) fibre in its purified form for decolorization of dye-containing effluent from a down-flow hanging sponge (DHS) reactor. Batch adsorption experiments were conducted by varying adsorbent dose, solution pH, contact time and temperature. The results showed that the adsorption percentage of colour increased with increasing in adsorbent dosage from 0.1 g to 1.3 g, solution pH from 2 to 10 and contact time from 1 h to 72 h. The adsorption process was sensitive to temperature and the adsorption percentage of colour reached the highest value at 30°C but decreased when temperature increased from 30°C to 60°C. Purified coconut fibre (PCF) had a good adsorption capacity under the optimal conditions of an adsorbent dose of 0.7 g, pH 8, temperature of 30°C and 24 h contact time. The equilibrium data were well fitted to both Langmuir and Freundlich isotherms, and the best fit of equilibrium isotherms was described using the Freundlich isotherm model. The Langmuir maximum adsorption capability of the PCF was found to be 303 (Pt/Co)/g at 30°C. The results of this study indicated the applicability of PCF as post-treatment unit of DHS reactor for removal of colour in the industrial dye effluent.

Carbon Waste Powder Prepared from Carbon Rod Waste of Zinc-Carbon Batteries for Methyl Orange Adsorption

A research on the preparation of Carbon Waste Powder, CWP, was conducted and made from carbon rod waste which was extracted from used zinc-carbon batteries. This research was an effort to overcome environmental problem caused by battery waste by converting into adsorbent for methyl orange (MO) that frequently used by textile industries. The prepared powder was then analyzed to understand its characteristic peaks, crystallinity, and to compare the properties with other carbonaceous forms, i.e. a commercial Carbon Paper (CP), and a commercial meso- carbon micro-beads (MCMB). The analysis found that CWP is dominated by graphitic carbon. An adsorption experiment was then conducted to study their adsorption ability to methyl orange solution. The result found that those three carbonaceous materials have the ability to adsorb methyl orange with different activities. MCMB has the highest adsorption capacity of 0.197 mg.g-1. Meanwhile, CWP and CP show adsorption capacity of 0.066 mg.g-1 and 0.062 mg.g-1, respectively. Methyl orange adsorption on CWP and CP were under second order, which means the adsorption could be four times faster as the MO solution doubled. Moreover, the rate constant of MO adsorption on CWP is 8×10-4 min-1, which was higher than the rate constant of MO adsorption on CP. It confirmed that the CWP can be used as a promising adsorbent for dye waste water. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Ternary Composite of Co-Doped CdSe@electrospun Carbon Nanofibers: A Novel Reusable Visible Light-Driven Photocatalyst with Enhanced Performance

In this work, flexible ternary composites of cobalt-doped cadmium selenide/electrospun carbon nanofibers (Co-CdSe@ECNFs) for photocatalytic applications were fabricated successfully via electrospinning, followed by carbonization. For the fabrication of the proposed photocatalysts, Co-CdSe nanoparticles were grown in situ on the surface of ECNFs during the carbonization of precursor electrospun nanofibers obtained by dispersing Se powder in the electrospinning solution of polyacrylonitrile/N,N-Dimethylformamide (PAN/DMF) containing Cd2+ and Co2+. The photocatalytic performance of synthesized samples is investigated in the photodegradation of methylene blue (MB) and rhodamine B (RhB) dyes. Experimental results revealed the superior photocatalytic efficiency of Co-CdSe@ECNFs over undoped samples (CdSe@ECNFs) due to the doping effect of cobalt, which is able to capture the photogenerated electrons to prevent electron–hole recombination, thereby improving photocatalytic performance. Moreover, ECNFs could play an important role in enhancing electron transfer and optical absorption of the photocatalyst. This type of fabrication strategy may be a new avenue for the synthesis of other ECNF-based ternary composites.

Removal of bromophenol blue anionic dye from water using a modified exuviae of Hermetia illucens larvae as biosorbent

Organic dyes originating from liquid effluents from the textile industries are harmful to the environment. They are toxic and reduce the penetration of light into aquatic environments. In this study, a biosorbent was produced from the exuviae of Hermetia illucens (Linnaeus) larvae and used to remove organic anionic dyes from an aqueous medium. The solids were characterized in terms of thermal stability, chemical structure, morphology, and porosity using thermogravimetric (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and N₂ adsorption-desorption. There were studied the effects of pH and dosage of the adsorbent on the adsorption of the bromophenol blue dye, used as a model molecule. The adsorption kinetics was studied with Lagergren's pseudo-first-order rate model. The maximum adsorbed amount was 571 mg g^-1 according to Langmuir's model. The adsorption process was evaluated as exothermic and spontaneous and was classified as physical adsorption. The prepared biosorbent was tested in five consecutive adsorption cycles achieving 99% dye removal at each stage. This demonstrated the maintenance of adsorption efficiency and desorption capacity. These results suggest that prepared biosorbent have potential applications in the treatment of effluents from textile industries.

Dye Removal Using Hairy Nanocellulose: Experimental and Theoretical Investigations

Adsorption is a common technique for the treatment of dye-contaminated wastewater. Achieving a high dye removal capacity is a common challenge with sustainable, low-cost adsorbents. Recently, a class of easily functionalized, biorenewable cellulose nanoparticles called hairy nanocellulose has been developed. Electrosterically stabilized nanocrystalline cellulose (ENCC), which can be synthesized from wood pulp through a two-step oxidation by periodate and chlorite, is a form of hairy nanocellulose with a high negative charge density, and thus has the potential for a high adsorption capacity. In this work, the adsorption of methylene blue, a cationic dye, by ENCC was shown to occur up to charge stoichiometry (1400 mg dye/g adsorbent), at which point aggregation of ENCC-dye complexes is observed. A model is developed to show that the adsorption can be described by an ion-exchange mechanism and is influenced by the presence of other ions. Equilibrium dye removal is reduced at both high ionic strengths and low pH. To facilitate handling, composite hydrogel beads of sodium alginate and ENCC (ALG-ENCC beads) are developed, and their methylene blue removal capacity is shown to maintain a high removal capacity (1250 mg/g). ALG-ENCC beads provide a facile way to employ these nanoparticles on a larger scale, providing a potential means for the removal of dyes and other contaminants at larger wastewater volumes.

Preparation of Polyaniline/Emulsion Microsphere Composite for Efficient Adsorption of Organic Dyes

Surface-functionalized polymeric microspheres have wide applications in various areas. Herein, monodisperse poly(styrene-methyl methacrylate-acrylic acid) (PSMA) microspheres were prepared via emulsion polymerization. Polyaniline (PANI) was then coated on the PSMA surface via in situ polymerization, and a three-dimensional (3D) structured reticulate PANI/PSMA composite was, thus, obtained. The adsorption performance of the composite for organic dyes under different circumstances and the adsorption mechanism were studied. The obtained PANI/PSMA composite exhibited a high adsorption rate and adsorption capacity, as well as good adsorption selectivity toward methyl orange (MO). The adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm. The maximum adsorption capacity for MO was 147.93 mg/g. After five cycles of adsorption-desorption, the removal rate remained higher than 90%, which indicated that the adsorbent has great recyclability. The adsorbent materials presented herein would be highly valuable for the removal of organic dyes from wastewater.

Water Contaminated by Industrial Textile Dye: Study on Decolorization Process

This work aims to investigate possible interferences due to the presence of sodium carbonate on the photodegradation of the reactive Black 5 azoic dye, both in systems containing only titanium oxide and those containing titanium oxide and hydrogen peroxide. The role of hydrogen peroxide is explicitly treated. Sodium carbonate, in fact, is often present in the wastewater of textile industries as it is used in the fiber dyeing phases. The use of TiO2 nanoparticles is emphasized, and the possible danger is underlined. Each system was subjected to ultraviolet irradiation (UV) by varying the exposure time. After the photodegrading tests, the resulting solutions were analyzed by UV-vis spectrophotometry and High-Resolution Nuclear Magnetic Resonance to measure the residual concentrations of dye. The dye degradation curves and reaction rates for different UV exposure times were obtained and discussed as a function of the used additives. All the data are repeated three times, and they differ only by a maximum of 5%. The results indicated a reduction of about 50% of the initial concentration of Reactive Black 5 after 30 min under optimal experimental conditions. The NMR analysis indicated the formation of a series of aromatic structures that were generated by the UV-induced photochemical fragmentation of the original molecule.