Recent advances for dyes removal using novel adsorbents: A review

Adsorption of reactive blue 49 onto cross-linked chitosan-based composites containing waste mussel shell and waste active sludge char

Cross-linked chitosan/waste mussel shell (C/WMS) and chitosan/waste mussel shell/waste active sludge char (C/WMS/WASC) composites were prepared from waste mussel shell, waste active sludge (WAS), and chitosan, and cross-linked with glutaraldehyde. The quantities of chitosan, WMS, and WASC used for the C/WMS and C/WMS/WASC composites were 1:1 and 1:0.5:0.5, respectively. The two adsorbents were characterized for their quality by a scanning electron microscope (SEM), an energy-dispersive X-ray spectroscopy (EDX), and a Brunauer, Emmett and Teller (BET) analyzer. The effects of contact time (0-1,620 mins), pH (1-5), adsorbent dosage (0.01-0.1 g/50 ml), initial dye concentration (20-100 mg/L), and temperature (25-45 °C) on Reactive Blue 49 (RB49) adsorption onto C/WMS and C/WMS/WASC composites were investigated. The maximum RB49 adsorption capacity of C/WMS and C/WMS/WASC composites was 54.7 and 38.8 mg/g, respectively. The experimental data were analyzed by kinetic and isotherm models. The Freundlich isotherm was a good fit for the experimental data of RB49 adsorption on C/WMS and C/WMS/WASC composites, and the adsorption kinetics for both adsorbents were the pseudo-second-order rate equation. All results showed the preparative adsorbents can be used as effective adsorbents for the treatment of waste water contaminated with RB49 since they are low cost and eco-friendly for the environment.

A Mini Review on Antiwetting Studies in Membrane Distillation for Textile Wastewater Treatment

The textile industry is an important contributor to the growth of the global economy. However, a huge quantity of wastewater is generated as a by-product during textile manufacturing, which hinders the ongoing development of textile industry in terms of environmental sustainability. Membrane distillation (MD), which is driven by thermal-induced vapor pressure difference, is being considered as an emerging economically viable technology to treat the textile wastewater for water reuse. So far, massive efforts have been put into new membrane material developments and modifications of the membrane surface. However, membrane wetting, direct feed solution transport through membrane pores leading to the failure of separation, remains as one of the main challenges for the success and potential commercialization of this separation process as textile wastewater contains membrane wetting inducing surfactants. Herein, this review presents current progress on the MD process for textile wastewater treatment with particular focuses on the fundamentals of membrane wetting, types of membranes applied as well as the fabrication or modification of membranes for anti-wetting properties. This article aims at providing insights in membrane design to enhance the MD separation performance towards commercial application of textile wastewater treatment.

Electrospun-based TiO2 nanofibers for organic pollutant photodegradation: a comprehensive review

Titanium dioxide (TiO2) is commonly used as a photocatalyst in the removal of organic pollutants. However, weaknesses of TiO2 such as fast charge recombination and low visible light usage limit its industrial application. Furthermore, photocatalysts that are lost during the treatment of pollutants create the problem of secondary pollutants. Electrospun-based TiO2 fiber is a promising alternative to immobilize TiO2 and to improve its performance in photodegradation. Some strategies have been employed in fabricating the photocatalytic fibers by producing hollow fibers, porous fibers, composite TiO2 with magnetic materials, graphene oxide, as well as doping TiO2 with metal. The modification of TiO2 can improve the absorption of TiO2 to the visible light area, act as an electron acceptor, provide large surface area, and promote the phase transformation of TiO2. The improvement of TiO2 properties can enhance carrier transfer rate which reduces the recombination and promotes the generation of radicals that potentially degrade organic pollutants. The recyclability of fibers, calcination effect, photocatalytic reactors used, operation parameters involved in photodegradation as well as the commercialization potential of TiO2 fibers are also discussed in this review.

Attapulgite as a skeleton for the fabrication of magnetic structural-functional materials with a superhydrophobic shell

Fabrication of structural-functional materials endowed with unique features from attapulgite, and which may be provided a well structural platform for diversified applications, such as adsorbent for organic pollutants, the superhydrophobic coating and water/oil separation.

Eichhornia crassipes (Mart.) Solms (natural or carbonized) as biosorbent to remove pollutants in water

The prolific aquatic herb Eichhornia crassipes considered a pest in many countries can cause damage such as obstruction of water flows and impair the locomotion of fishing boats. However, E. crassipes is renewable, inexpensive, and widely available in nature, and its ability to adsorb recalcitrant pollutants with mutagenic and carcinogenic properties, including synthetic dyes and heavy metals, has been extensively studied by the scientific community. This review paper analyzes previous reports concerning the use of E. crassipes (in the natural and carbonized form) as an adsorbent for heavy metal cations and textile dye. The adsorptive capacity of E. crassipes, the best conditions (adsorbent dosage, pH, and temperature) for the removal of these pollutants, the mechanism of adsorption, and the comparison between natural and carbonized forms (advantages and disadvantages) are discussed. All the results revised in this review indicated that the use of E. crassipes (and its carbon derived) as adsorbent is promising and is an excellent material to be applied in the water treatment. It could be used in the actual technologies for the treatment of contaminated water by heavy metals and textile dyes; however, more studies need to be made on scale-up, economy projects, and related issues, to be finally implemented in wastewater treatment plants.

Removal of methylene blue and lead(ii) via PVA/SA double-cross-linked network gel beads loaded with Fe3O4@KHA nanoparticles

The adsorption of MB and Pb(ii) onto and regeneration of PVA/SA/Fe₃O₄@KHA magnetic gel beads.

Zinc-bearing dust derived non-toxic mixed iron oxides as magnetically recyclable photo-Fenton catalyst for degradation of dye

In this paper, comprehensive utilization of hazardous zinc-bearing dust for preparation of non-toxic mixed iron oxides as a magnetically recyclable photo-Fenton catalyst for degradation of dye by a facile solid state reaction process was proposed. The as-prepared samples were characterized by X-ray diffraction (XRD), Raman spectra, ultraviolet and visible (UV-Vis) spectra and Physical Property Measurement System (PPMS), and the degradation performance of as-prepared catalysts was also tested and analyzed. The results show that spinel ferrite coexisting with or without Fe₂O₃ was the predominant phase in the as-prepared samples, which were confirmed by Raman analysis. The as-prepared samples presented high degradation efficiency (about 90%) of rhodamine B (RhB) in the presence of hydrogen peroxide (H₂O₂) with visible light irradiation, owing to the synergistic effect of photocatalyst reaction and Fenton-like catalyst reaction during the degradation process. The mixed iron oxides also presented stable structure and exhibited excellent reusability with a degradation efficiency of 87% after the fifth cycle of reuse. Importantly, the heavy metals in the zinc-bearing dust could be fixed in the stable spinel structure. This paper could provide a simple approach for comprehensive utilization of zinc-bearing dust to synthesize non-toxic mixed iron oxides as a magnetically recyclable photo-Fenton catalyst for degradation of dye.

Reticular synthesis of two anionic Zn(ii)-MOFs for organic dye adsorption/separation and lanthanide ion sensitization

Two new pillar-layered anionic microporous Zn(ii)-MOFs have been reticularly synthesized and developed as multifunctional materials for adsorption and separation of organic dyes and sensitization of rare earth ions.

Functionalized polyurethane sponge based on dopamine derivative for facile and instantaneous clean-up of cationic dyes in a large scale

Functionalized sponge adsorbent was prepared by a mussel-inspired strategy, which achieved successive modification of material and remained the properties of substrate. The dopamine derivative, DOPAm, was synthesized and adhered to polyurethane (PU) sponge before in situ polymerization with sodium p-styrenesulfonate. The adsorbent showed superior removal efficiency for cationic dyes (98.9 % for methylene blue (MB) at the concentration of 200 μmol/L); it took 1 s only for the adsorbent to adsorb the dyes by swelling and squeezing out the bulk solution simply. Meanwhile, the superior adsorption effect of the adsorbent could be maintained in a wide range of solution pH values from 1 to 13 at room temperature (293 K) in several repeat experiments, due to the slight influence of strong acid and alkali on polysulfonate. With unchanged other experimental conditions, the removal efficiency is still more than 90 % after reusing for 10 times at the different concentrations of MB dye solutions (50, 100, 200 μmol/L). For large-scale wastewater treatment, with the removal efficiency of 80.0 %, the adsorbent could purify 4.1 L wastewater containing MB dye (100 μmol/L) with the maximum flux of 22.2 L/(m³·s) without the assistance of any equipment except for a vacuum pump. Therefore, the adsorbent has great possibilities to be applied in high-efficient and convenient treatment of wastewater in a large scale.

Efficiency of Sawdust as Low-Cost Adsorbent for Dyes Removal

In recent years, the removal of dyes from wastewater has attracted considerable attention due to their harmful effects to ecosystem and human health. Adsorption as a facile and effective technique has been widely used to eliminate a large variety of dyes from aqueous solutions. Activated carbon is the most preferred adsorbent to treat wastewater but its use is limited because of high cost. Therefore, several low-cost and natural materials and wastes have been used as precursors for the preparation of alternative adsorbents. Among them, sawdust as an abundant and low-cost by-product has been explored as adsorbent for the removal of dyes from wastewater. This review focuses on the various sawdust used as a precursor for the preparation of activated carbons. Extensive literature information about sawdust, its compositions, activation methods, its efficiency for dyes removal, and environmental conditions effects has been reviewed. The applicability of various adsorption kinetic models and adsorption isotherm models for dye removal by sawdust-derived activated carbons has been also reported. Finally, this paper highlights the use of sawdust as base material for various composites and mixture which can be used as granular activated carbon.

Fabrication of Zn-based magnetic zeolitic imidazolate framework bionanocomposite using basil seed mucilage for removal of azo cationic and anionic dyes from aqueous solution

The Basil seeds mucilaginous polysaccharide exhibits remarkable physical and chemical properties like high water-absorbing capacity, emulsifying, and stabilizing properties. The metal-organic frameworks are one of the most promising precursors made of metal clusters and organic connectors for the fabrication of advanced adsorbents due to their unique properties. In this study, the bionanocomposite of magnetic zeolitic imidazolate framework-8 was successfully synthesized and applied to adsorb azo cationic and anionic dyes. The synthesized magnetite nanoparticles were pretreated with mucilage extracted from basil seeds to acquire negatively charged magnetite surface, followed by nucleation through attracting zinc cation, and then the growth of metal-organic frameworks which yields high-quality ZIF-8 crystals. The samples were characterized by Field Scanning Electron Microscopy, X-ray Diffraction, Fourier Transform Infrared Spectrometry, vibrating sample magnetometer, and Brunauer-Emmett-Teller surface area analysis. In the process of adsorption, influencing factors and recycling regeneration were discussed, and the adsorption mechanisms such as kinetics, isotherm, and thermodynamics were explored. The results of the adsorption process showed that maximum adsorption capacities were 9.09 and 13.21 mg/g for Methylene blue and Eriochrome Black T, respectively. The excellent reusability combined with its magnetic separation property makes the nanocomposite a promising adsorbent for the removal of cationic and anionic dyes.

Glycerol mediated solution combustion synthesis of nano magnesia and its application in the adsorptive removal of anionic dyes

This study reports solution combustion synthesis of magnesia nanoparticles (nMgO) using magnesium nitrate as oxidiser and glycerol as fuel. Size, morphology, crystal structure and surface properties of synthesised nMgO were analysed by PXRD, SEM, TEM, FTIR and Point of Zero Charge. The XRD pattern of nMgO confirmed prepared samples were single cubic-phase without any impurities. TEM analysis proved nMgO was in nano regime with an average particle diameter of 20–40 nm. FTIR spectra show the presence of characteristic peaks of nMgO and support the XRD results. The prepared nMgO was employed as an adsorbent for the removal of two anionic dyes viz. Indigo Carmine (IC) and Orange G (OG). Furthermore, various adsorption isotherms and kinetic models were performed to understand the kinetics and mechanism of the adsorption process. Experimental results demonstrated that the adsorption equilibrium data fit well to Sips isotherm (R2 > 0.98) and the saturated adsorption capacities of nMgO were found to be 262 mg g−1 for IC and 126 mg g−1 for OG. Adsorption kinetics analysis revealed that the adsorption followed pseudo-first-order model, with both film and pore diffusion governing the rate of adsorption. Excellent adsorption capacity combined with efficient regeneration proved the potential of the prepared nMgO as an adsorbent for the removal of harmful dyes from industrial effluent.

Uptake of micropollutant-bisphenol A, methylene blue and neutral red onto a novel bagasse-β-cyclodextrin polymer by adsorption process

The presence of emerging micropollutants and dyes in water resource has raised global concern about their intense effects to aquatic environments, ecosystem and human health in general. So far, various adsorbents have been suggested for reducing the levels of bisphenol A, methylene blue and neutral red contamination in wastewaters. However, a number of these adsorbents seemed to have low adsorptive capacities and regeneration performances. In view of these, batch experiment was performed to decontaminate these pollutants from aqueous solutions using an optimized bagasse-β-cyclodextrin polymer (SB-β-CD). Characterization studies of SB-β-CD were performed using FTIR, pH point of zero charge, XRD and BET methods. Adsorption of BPA, MB and NR was favored at lower temperature (298 K) and pH of 7.0, 9.0 and 6.0, respectively. The maximum adsorption capacity of BPA, MB and NR at 298 K was 121, 963 and 685 mg g^-1, respectively. Hydrogen bonding through host-guest inclusion and electrostatic interactions could respectively attribute to uptake of BPA and MB/NR onto SB-β-CD. Adsorption kinetics of three pollutants followed pseudo-second-order model. Langmuir and Freundlich models were fitted to describe the adsorption of BPA and MB/NR, respectively. Thermodynamic parameters confirmed the occurrence of physical adsorption which is spontaneous and exothermic in nature. SB-β-CD loaded with BPA and MB/NR was certainly reused by 75% ethanol and 0.1 mol L^-1 HCl solutions, respectively. Novel SB-β-CD showed better adsorptive capacity and regeneration performances; consequently can offers practical application for removal of BPA, MB and NR from wastewaters.

Adsorption of copper ions from solution using xanthate wheat straw

To enhance adsorption capacity of wheat straw (WS) toward copper ion from solution, carbon disulfide was used to modify WS by a facile grafting method through epichlorohydrin and ethylenediamine. So WS containing xanthate groups (XWS) was obtained. The XWS was characterized using elemental analysis, X-ray diffraction, infrared spectroscopy and adsorption property of XWS toward copper ions. The results showed that S was introduced into the surface of WS. The solution pH was in favor of Cu²⁺ adsorption at pH 5, while NaCl existing in solution was slightly favorable for adsorption. The adsorption kinetic followed the pseudo-second-order kinetic model, while the adsorption isotherm curve was well fitted using the Langmuir model. The adsorption capacity was 57.5 mg·g^-1 from experiment. The process was entropy-produced, endothermic and spontaneous in nature. The column adsorption was performed and Yan model was good to predict the breakthrough curve. XWS as adsorbent is promising to remove copper ions from solution, and this offers one way of effective utilization of waste byproduct from agriculture.

An economical and effective alternative to commercial activated carbon for treatment of synthetic dye pollution in aquatic environment: surfactant modified waste product of Zostera marina

In this study, a novel biosorbent material was created from the waste product of Zostera marina with the surfactant modification (Hexadecyltrimethylammonium bromide) and tried as a potential alternative to commercial (powdered) activated carbon for the treatment of synthetic dye (Fast green FCF, triarylmethane (anionic) type) pollution in aquatic environment. The treatment capability of biosorbent material was evaluated by the parameter optimization, kinetic, thermodynamic, equilibrium and characterization experiments. The optimum treatment conditions were found to be pH of 3, biosorbent amount of 10 mg, synthetic dye concentration of 15 mg L^-1, temperature of 45 °C and operation time of 360 min. It was determined that Elovich model was the most suitable model among the models used to define the biosorption kinetic data. The synthetic dye treatment process was endothermic and spontaneous. Freundlich model best explained the biosorption isotherm data. The biosorbent has very heterogeneous surface with the different functional groups. The treatment capabilities of prepared biosorbent and activated carbon under the same operating conditions were calculated to be 163.075 and 110.635 mg g^-1, respectively. Hereby, these experimental findings show that the synthesized eco-friendly and low-cost biosorbent can be a powerful alternative to commercial activated carbon for the purification of synthetic dye pollution in water environment.

Facile One-Pot Biogenic Synthesis of Cu-Co-Ni Trimetallic Nanoparticles for Enhanced Photocatalytic Dye Degradation

Biomolecules from plant extracts have gained significant interest in the synthesis of nanoparticles owing to their sustainable properties, cost efficiency, and environmental wellbeing. An eco-friendly and facile method has been developed to prepare Cu-Co-Ni trimetallic nanoparticles with simultaneous bio-reduction of Cu-Co-Ni metal precursors by aqueous extract of oregano (Origanum vulgare) leaves. Dramatic changes in physicochemical properties of trimetallic nanoparticles occur due to synergistic interactions between individual metal precursors, which in turn outclass the properties of corresponding monometallic nanoparticles in various aspects. The as biosynthesized Cu-Co-Ni trimetallic nanoparticles were initially analyzed using ultraviolet (UV)–visible spectroscopy. The morphology, structure, shape, and size of biosynthesized trimetallic nanoparticles were confirmed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) spectroscopy. The elemental analysis was carried out by energy-dispersive X-ray (EDX) spectroscopy. Fourier transform infrared (FTIR) microscopy was carried out to explain the critical role of the biomolecules in the Origanum vulgare leaf extract as capping and stabilizing agents in the nanoparticle formation. Additionally, simultaneous thermogravimetric analysis (TGA) and differential thermogravimetry (DTG) analysis was also performed to estimate the mass evaluation and rate of the material weight changes. The photocatalytic activity of as biosynthesized trimetallic nanoparticles was investigated towards methylene blue (MB) dye degradation and was found to be an efficient photocatalyst for dye degradation. Kinetic experiments have shown that photocatalytic degradation of MB dye followed pseudo-first-order kinetics. The mechanism of the photodegradation process of biogenic Cu-Co-Ni trimetallic nanoparticles was also addressed.

Elimination of basic blue 9 by electrocoagulation coupled with pelletized natural dead leaves (Sapindus mukorossi) biosorption

Elimination of basic blue 9 (BB-9), a cationic textile dye, by electrocoagulation coupled with biosorption exploiting pelletized natural dead leaves (PNDL) of Sapindus mukorossi, an economic alternative biosorbent, was investigated. The experimental runs were conducted in a laboratory-scale hybrid reactor loaded with Al electrodes, aeration spargers and PNDL packed twin suspended buckets. The pelletized adsorbents offer key advantages of good mechanical stability, lesser clogging risk, and easy disengagement as compared to powdered adsorbents. The parameters of current density, pH, PNDL dose, and initial dye concentration were studied for the decolorization and COD removal efficiency. The experimental results revealed that up to 99.9% decolorization and 90.01% COD removal efficiency achieved after 8 min at optimum condition of current density (j)=20.27 mA/cm², pH = 9, PNDL dose = 6 g/L, and initial dye concentration = 50 mg/L. The BB-9 elimination followed the first-order kinetics with K₁=0.318 min^-1 and R²=0.997. The results revealed the potential of PNDL as a feasible biosorbent with the effective performance of the coupled process.

Treatment of textile dyes using advanced oxidative and adsorptive processes individually and combined: study of the operational parameters, kinetic and adsorptive equilibrium

Advanced oxidative processes (AOP) have been consolidated as an efficient treatment technique to degrade persistent contaminants. In addition to them, biosorption also emerges as a technique capable of removing both pollutants and intermediate products generated by other treatments such as AOP. Thus, this work evaluated the degradation and removal of the mixture of dyes Direct Red 23 and Direct Red 227 in aqueous solution (50 mg·L^-1 of each). Preliminary tests showed that the photo-Fenton system under sunlight radiation was the most efficient, reaching a degradation ≥93%. For the adsorptive process using chicken eggshell, preliminary tests indicated that the ideal dosage of adsorbent was 8.0 g·L^-1. For this process, a factorial design indicated the best working conditions, which demonstrated from the system adjusted well to the Elovich (kinetic) model and to the Freundlich and Sips models (equilibrium). When associating the two processes, AOP followed by adsorption achieved a total degradation/removal of ≈98% (for all λ) in a time of 60 min. Thus, the feasibility of the combined treatment is indicated.

Current Development in Decolorization of Synthetic Dyes by Immobilized Laccases

The world today is in a quest for new means of environmental remediation as the methods currently used are not sufficient to halt the damage. Mostly, a global direction is headed toward a shift from traditional chemical-based methods to a more ecofriendly alternative. In this context, biocatalysis is seen as a cost-effective, energy saving, and clean alternative. It is meant to catalyze degradation of recalcitrant chemicals in an easy, rapid, green, and sustainable manner. One already established application of biocatalysis is the removal of dyes from natural water bodies using enzymes, notably oxidoreductases like laccases, due to their wide range of substrate specificity. In order to boost their catalytic activity, various methods of enhancements have been pursued including immobilization of the enzyme on different support materials. Aside from increased catalysis, immobilized laccases have the advantages of higher stability, better durability against harsh environment conditions, longer half-lives, resistance against protease enzymes, and the ability to be recovered for reuse. This review briefly outlines the current methods used for detoxification and decolorization of dye effluents stressing on the importance of laccases as a revolutionary biocatalytic solution to this environmental problem. This work highlights the significance of laccase immobilization and also points out some of the challenges and opportunities of this technology.

Kinetic Studies on the Catalytic Degradation of Rhodamine B by Hydrogen Peroxide: Effect of Surfactant Coated and Non-Coated Iron (III) Oxide Nanoparticles

Iron (III) oxide (Fe₃O₄) and sodium dodecyl sulfate (SDS) coated iron (III) oxide (SDS@Fe₃O₄) nanoparticles (NPs) were synthesized by the co-precipitation method for application in the catalytic degradation of Rhodamine B (RB) dye. The synthesized NPs were characterized using X-ray diffractometer (XRD), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infra-red (FT-IR) spectroscopy techniques and tested in the removal of RB. A kinetic study on RB degradation by hydrogen peroxide (H₂O₂) was carried out and the influence of Fe₃O₄ and SDS@Fe₃O₄ magnetic NPs on the degradation rate was assessed. The activity of magnetic NPs, viz. Fe₃O₄ and SDS@Fe₃O₄, in the degradation of RB was spectrophotometrically studied and found effective in the removal of RB dye from water. The rate of RB degradation was found linearly dependent upon H₂O₂ concentration and within 5.0 × 10^-2 to 4.0 × 10^-1 M H₂O₂, the observed pseudo-first-order kinetic rates (k_obs, s^-1) for the degradation of RB (10 mg L^-1) at pH 3 and temperature 25 ± 2 °C were between 0.4 and 1.7 × 10⁴ s^-1, while in presence of 0.1% w/v Fe₃O₄ or SDS@Fe₃O₄ NPs, k_obs were between 1.3 and 2.8 × 10⁴ s^-1 and between 2.6 and 4.8 × 10⁴ s^-1, respectively. Furthermore, in presence of Fe₃O₄ or SDS@Fe₃O₄, k_obs increased with NPs dosage and showed a peaked pH behavior with a maximum at pH 3. The magnitude of thermodynamic parameters E_a and ΔH for RB degradation in presence of SDS@Fe₃O₄ were 15.63 kJ mol^-1 and 13.01 kJ mol^-1, respectively, lowest among the used catalysts, confirming its effectiveness during degradation. Furthermore, SDS in the presence of Fe₃O₄ NPs and H₂O₂ remarkably enhanced the rate of RB degradation.

New Eco-Materials Derived from Waste for Emerging Pollutants Adsorption: The Case of Diclofenac

This work proposes new eco-materials for the adsorption of diclofenac (DCF). The large consumption of this nonsteroidal anti-inflammatory drug combined with the inefficiency of wastewater treatment plants (WWTPs) leads to its presence in aquatic environments as an emerging pollutant. The adsorption technique is widely used for pharmaceutical removal. Moreover, due to the large effect of commercial adsorbents, in the frame of the Azure Chemistry approach, new sustainable materials are mandatory for removal as emerging pollutants. The work proposes three adsorbents that were obtained from different stabilization methods of fly ash derived from an incinerator plant; the stabilization techniques involved the use of various industrial by-products such as bottom ash, flue gas desulphurization residues, coal fly ash, and silica fume. The best performance, although less than activated carbon, was obtained by COSMOS (COlloidal Silica Medium to Obtain Safe inert: the case of incinerator fly ash), with a removal efficacy of approximately 76% with 15 g/L of material. Several advantages are expected not only from the DCF removal but also from an economic perspective (the newly obtained adsorbents are eco-materials, so they are cheaper in comparison to conventional adsorbents) and in terms of sustainability (no toxic reagents and no heating treatment are involved). This work highlights the adsorption performance of the new eco-materials and their potential use in WWTPs.

Resuscitation, isolation and immobilization of bacterial species for efficient textile wastewater treatment: A critical review and update

Given highly complex and recalcitrant nature of synthetic dyes, textile wastewater poses a serious challenge on surrounding environments. Until now, biological treatment of textile wastewater using efficient bacterial species is still considered as an environmentally friendly and cost-effective approach. The advances in resuscitating viable but non-culturable (VBNC) bacteria via signaling compounds such as resuscitation-promoting factors (Rpfs) and quorum sensing (QS) autoinducers, provide a vast majority of potent microbial resources for biological wastewater treatment. So far, textile wastewater treatment from resuscitating and isolating VBNC state bacteria has not been critically reviewed. Thus, this review aims to provide a comprehensive picture of resuscitation, isolation and application of bacterial species with this new strategy, while the recent advances in synthetic dye decolorization were also elaborated together with the mechanisms involved. Discussion was further extended to immobilization methods to tackle its application. We concluded that the resuscitation of VBNC bacteria via signaling compounds, together with biochar-based immobilization technologies, may lead to an appealing biological treatment of textile wastewater. However, further development and optimization of the integrated process are still required for their wide applications.

Naturally available diatomite and their surface modification for the removal of hazardous dye and metal ions: A review

The presence of toxic pollutants such as dyes and metal ions at higher concentrations in water is very harmful to the environment. Removal of these pollutants using diatomaceous earth or diatomite (DE) and surface-modified DE has been extensively explored due to their excellent physio-chemical properties and low cost. Therefore, naturally available DE being inexpensive, their surface modified adsorbents could be one of the potential candidates for the wastewater treatment in the future. In this context, the current review has been summarized for the removal of both pollutants i.e., dyes and metal ions by surface-modified DE using the facile adsorption process. In addition, this review is prominently focused on the various modification process of DE, their cost-effectiveness; the physio-chemical characteristics and their maximum adsorption capacity. Further, real-time scenarios of reported adsorbents were tabulated based on the cost of the process along with the adsorption capacity of these adsorbents.

Carbon material-immobilized ionic liquids were applied on absorption of Hg2+ from water phase

In this study, several immobilized ionic liquid adsorbents on carbon materials were synthesized with impregnation method. The carrier materials were activated carbon and three kinds of multi-walled carbon nanotubes. And the synthetic adsorbents immobilized different kinds of ionic liquids were characterized by Boehm titration, FT-IR, XPS, TG, and BET analysis, respectively. Finally, carbon materials after [C4mim]HSO₄ immobilization were selected as adsorbent to remove Hg²⁺ from water phase. The optimum conditions of adsorption test of ionic liquid immobilized by multi-walled carbon nanotubes were as follows: the initial concentration of Hg²⁺ was 400 mg/L, the adsorbent addition amount was 40 mg, the temperature was 20 °C, the reaction time was 200 min, the removal rate of Hg²⁺ peaked at 62.95%, the adsorption capacity was reached 79.00 mg/g. The optimum conditions of adsorption test of ionic liquid immobilized by activated carbon were as follows: the initial concentration of Hg²⁺ was 300 mg/L, the adsorbent addition amount was 0.2 g, the temperature was 20 °C, pH was 2.0, the reaction time was 100 min, the removal rate of Hg²⁺ was more than 99%, the adsorption capacity was 118.65 mg/g. The adsorption isotherm fitting study found that the adsorption of adsorbent on Hg²⁺ was more in line with the Langmuir model, and the adsorption kinetics study shows that the adsorption process is consistent with the pseudo-second-order kinetic equation. The results of kinetic analysis are further verified by thermodynamic analysis.

Conversion of MDF wastes into a char with remarkable potential to remove Food Red 17 dye from aqueous effluents

Medium density fiberboard (MDF) wastes were converted into an efficient char able to uptake Food Red 17 dye (FR17) from colored effluents. The yield of the pyrolysis process, in terms of char, was 29%. The produced char presented micro and mesoporous, with surface area of 218.8 m² g^-1 and total pore volume of 0.122 cm³ g^-1. Regarding to the FR17 adsorption, removal percentages of 90% were found at pH 2 and using 0.5 g L^-1 of char. Pseudo-first and pseudo-second order models were adequate to represent the adsorption kinetic profile, being the equilibrium reached within 20 min. Freundlich model was selected to represent the equilibrium data. The maximum adsorption capacity was 210 mg g^-1. The adsorption of FR17 on the char was endothermic and physical in nature. The char was efficient for 8 adsorption-desorption cycles, maintaining the same adsorption capacity. In brief, this work demonstrated a useful practice in terms of cleaner production. It was possible add value to MDF wastes, generating an efficient and reusable adsorbent to treat colored effluents containing FR 17 dye.

Fe3O4/graphene aerogels: A stable and efficient persulfate activator for the rapid degradation of malachite green

Encapsulation metal oxides into carbon frameworks is a good strategy to synthesis high activity and stable catalyst. Here, Fe₃O₄ nanoparticles (∼20 nm) were firmly encapsulated in the graphene aerogels by a simple and environmentally friendly method (Fe₃O₄/GAs), for activating persulfate (PS) to degrade malachite green (MG) under simulated sunlight. A strong electron conduction was generated between the Fe₃O₄ nanoparticles and graphene sheets to improve the cycle of Fe(II)/Fe(III), and the MG degradation over a wide pH rage (3-9) was enhanced greatly. The MG molecule was decomposed into 12 intermediates and two possible pathways was proposed. More importantly, toxicity test and Toxicity Estimation Software (T.E.S.T.) proved that the toxicity of MG can be effectively controlled by Fe₃O₄/GAs + PS + light system. In addition to the high catalytic activity, Fe₃O₄/GAs exhibited a good stability and reusability due to the strong interaction between Fe₃O₄ and graphene layers. The degradation efficiency remained above 87% after six cycles, and the leaching amount of iron in each cycle was less than 0.125 wt%. SO₄•^- was the dominate radical for MG degradation and the heterogeneous Fenton-like reaction was mainly performed on the surface of catalyst. This work lay a foundation for applying Fe₃O₄/GAs as a highly efficient, stable and reusable heterogeneous Fenton-like catalyst for future applications.

Effects of charge density and molecular weight of papermaking sludge-based flocculant on its decolorization efficiencies

The charge densities (CD) and molecular weights (MW) of the flocculants are closely related to their application performances, but seldom researches focus on the effects of flocculant CD and MW on decolorization efficiencies. Herein, a series of flocculants with various CD and MW levels, named as PBF_1-9, were designed and synthesized from papermaking sludge. The physicochemical characteristics of the PBF_1-9 were measured by fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS) and particle charge density analyzer (PCD). The efficiencies of PBF_1-9 were studied in the reactive blue (RB) dye removals by flocculation under different process conditions. The operation costs of the flocculants were evaluated at their optimal dosages. Also, the pH-independences and ion-tolerances of the aforementioned flocculants were studied in terms of the molecular levels. The experimental results exhibited that the flocculants CD or MW values were relevant to their flocculation behaviors and operation costs. CD values played a dominant role in color removal efficiencies and the costs, whereas MW values were critical to the floc structure. The pH or ion-independences of the flocculants were significantly dependent on the CD and MW values. However, some conclusions, conflicted with prior studies, were observed in this work. For instance, flocculant with the highest CD and MW levels was not the most effective one in enduring pH variation and the coexisting ions. The floc properties, including floc size, resistance and recovery ability, were relatively insensitive to flocculant intrinsic CD and MW levels when the flocculants were used at their optimal dosages. Furthermore, the possible relevance between CD or MW levels and the flocculation mechanisms have been proposed in this work. Exploring the effects of flocculants CD and MW levels could precisely control the flocculant characteristics to achieve satisfactory decontamination efficiencies with low costs.