Adsorption of Cu (II), Pb (II) and Cr (VI) from aqueous solutions using black wattle tannin-immobilized nanocellulose

Periodate oxidation-mediated nanocelluloses: Preparation, functionalization, structural design, and applications

In recent years, the remarkable progress in nanotechnology has ignited considerable interest in investigating nanocelluloses, an environmentally friendly and sustainable nanomaterial derived from cellulosic feedstocks. Current research primarily focuses on the preparation and applications of nanocelluloses. However, to enhance the efficiency of nanofibrillation, reduce energy consumption, and expand nanocellulose applications, chemical pre-treatments of cellulose fibers have attracted substantial interest and extensive exploration. Various chemical pre-treatment methods yield nanocelluloses with diverse functional groups. Among these methods, periodate oxidation has garnered significant attention recently, due to the formation of dialdehyde cellulose derived nanocellulose, which exhibits great promise for further modification with various functional groups. This review seeks to provide a comprehensive and in-depth examination of periodate oxidation-mediated nanocelluloses (PONCs), including their preparation, functionalization, hierarchical structural design, and applications. We believe that PONCs stand as highly promising candidates for the development of novel nano-cellulosic materials.

Highly efficient removal of tannic acid from wastewater using biomimetic porous materials

To effectively remove tannic acid (TA) from wastewater, using green and natural materials has attracted increasing attention. Inspired by Galla Chinensis (GC) with high content of TA, this study synthesized a biomimetic porous adsorbent to mimic the GC structure using dialdehyde tapioca starch (DTS) and gelatin (GL). The TA adsorption performance and mechanism of synthetic porous material were investigated. Results revealed that the porous material exhibited a maximum TA adsorption capacity of 1072.01 mg/g, along with a high removal rate of 95.16% under the conditions of a DTS-GL mass ratio of 1:1, DTS aldehyde content of 48.16%, a solid content of 5%, and a pH of 2 at 25 °C. The adsorption of TA by DTS was not affected by water-soluble cationic and anion. The adsorption kinetics of TA on the porous material followed the pseudo-second-order model, and this Langmuir adsorption model (R2 = 0.9954) which were well described the adsorption of TA by the material, indicating that the adsorption primarily occurred in a monolayer. FTIR, XRD, DSC, TG, XPS, and SEM-EDS were employed to characterize the structure characteristics of the porous material. The cross-linking between DTS and GL by Schiff base reaction imparted a chemical structure could absorb TA by hydrogen bonding. The TA desorption rates of in 30% acetone and 40% ethanol solutions were 88.76% and 91.03%, respectively. The porous material prepared by the GC-inspired approach holds promise as an ideal choice for loading polyphenolic compounds and provides a new perspective for the design and application of bioinspired engineering materials.

Recent progress in tannin and lignin blended metal oxides and metal sulfides as smart materials for electrochemical sensor applications

Our technologically advanced civilization has made sensors an essential component. They have potential uses in the pharmaceutical sector, clinical analysis, food quality control, environmental monitoring, and other areas. One of the most active fields of analytical chemistry research is the fabrication of electrochemical sensors. An intriguing area of electroanalytical chemistry is the modification of electrodes using polymeric films. Due to their benefits, which include high adhesion to the electrode surface, chemical stability of the coating, superior selectivity, sensitivity, and homogeneity in electrochemical deposition, polymer-modified electrodes have attracted a great deal of interest in the electroanalytical sector. Conducting polymers are an important material for sensing devices because of their fascinating features, which include high mechanical flexibility, electrical conductivity, and the capacity to be electrochemically converted between electronically insulating and conducting states. Tannin or lignin nanomaterials can be an inter-linker leading to flexible and functional polymeric networks. There is a continuing demand for fast and simple analytical methods for the determination of many clinically important biomarkers, food additives, environmental pollutants etc. This review in a comprehensive way summarizes and discusses the various metal oxide and sulfide-incorporated tannin and lignin scaffolds using electrochemical sensing and biosensing.

Integration of wood-based components - Cellulose nanofibrils and tannic acid - into a poly(vinyl alcohol) matrix to improve functional properties

Poly(vinyl alcohol) (PVA) biocomposite films reinforced with cellulose nanofibrils (CNF) and biologically active tannic acid (TA) were prepared. The influence of different concentrations of CNF and TA in the PVA polymer matrix was investigated in terms of mechanical properties, thermal properties and hydrophobicity improvement of the prepared films. The results showed that in all cases the addition of CNF and TA improved the values of tensile strength and elastic modulus. The PVA film with 10 % CNF exhibited a 30 % higher tensile strength, and the three-component PVA film with 2 % CNF and 10 % TA (P2C10T) exhibited a 40 % higher tensile strength compared to the neat PVA film. The thermal properties (Tg, Tonset) of the PVA biocomposite films were greatly improved, with a significant effect observed for the three-component PVA films. The Tg of the PVA film with 10 % CNF and 10 % TA was 87 °C, 12 °C higher than that of the neat PVA film. For three-component PVA biocomposites with 4 % and 6 % CNF and with all weight percentages of TA, the Tonset shifted to a higher temperature range by about 30 °C compared to the neat PVA film. The PVA film with 2 % CNF and 10 % TA exhibited about a 20° higher contact angle than the neat PVA film. Moreover, the addition of both fillers to the PVA matrix resulted in PVA biocomposites with lower water absorption. PVA film with 10 % TA absorbed about 90 % less water and PVA film with 10 % CNF and 10 % TA absorbed about 80 % less water than the neat PVA film after the films were soaked in water for one hour. The better properties of the composite films produced are due to hydrogen and ester bonds between the components of the composite, which was confirmed by FT-IR spectroscopy. Antioxidant effective films were also obtained due to the biologically active TA to the PVA and PVA/CNF systems.

Removal of propranolol by membranes fabricated with nanocellulose/proanthocyanidin/modified tannic acid: The influence of chemical and morphologic features and mechanism study

Polymer-based membranes containing nanocellulose and natural macromolecules have potential to treat water, however few works have associated the changes in chemical and morphological membrane's features with their performance as adsorbent. Herein, a new green composite based on nanocellulose (NC) and alkylated tannic acid (ATA) and cross-linked with proanthocyanidin was produced and incorporated into polyacrylonitrile (PAN) membranes to eliminate propranolol (PRO) from water. Characterizations revealed that the increasing of NC-ATA content reduced the pore size of the membrane's upper surface and made the finger like structure of the sublayer disappear, due to the formation of hydrophilic domains of NC/ATA which speeds up the external solidification step. The presence of NC-ATA reduced the hydrophilicity, from a water contact angle of 3.65° to 16.51°, the membrane roughness, from 223.5 to 52.0 nm, and the zeta potential from -25.35 to -55.20 mV, improving its features to be a suitable adsorbent of organic molecules. The membranes proved to be excellent green adsorbent, tridimensional, and easy to remove after use, and qmax for PRO was 303 mg·g-1. The adsorption mechanism indicates that H-bonds, ion exchange, and π-π play important role in adsorption. NC-ATA@PAN kept high removal efficiencies after four cycles, evidencing the potential for water purification.

Effect of the magnetic core in alginate/gum composite on adsorption of divalent copper, cadmium, and lead ions in the aqueous system

The change of composition of an adsorbent material has been widely used as a method to increase its adsorption capacity, particularly concerning adsorbents made of polysaccharides. Introducing magnetic adsorbents into contaminated water treatment systems is a highly promising strategy, as it promotes the metal ions removal from water. Considering this, gum Arabic (GA) was associated with alginate (Alg), when magnetite nanoparticles were present or absent, to produce beads that were utilised to take up Cu(II), Cd(II), and Pb(II) from aqueous solution. After a complete characterisation (for which Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and swelling were used), the adsorption properties were established using batch and column tests. The magnetic beads (MAlg/GA) demonstrated improved adsorption in comparison with the beads made without magnetite (Alg/GA) under the same conditions. In normal adsorption conditions (pH 6.0, 25 °C, 2.5 g L-1 of adsorbent dosage), the highest uptake capacities recorded for the MAlg/GA beads were: for Cu(II), 1.33 mmol g-1; Cd(II), 1.59 mmol g-1; and for Pb(II), 1.43 mmol g-1. The pseudo-second-order kinetics and Langmuir isotherm models provided good fits for the adsorption of these metals. Overall, ion exchange and physical forces led to the uptake of these metals by both Alg/GA and MAlg/GA; moreover, the functional groups on the beads played crucial roles as binding sites. Additionally, it was observed that flow rates of >2 mL min-1 did not produce noticeable changes in uptake levels over the same flow period. It was found that the efficient eluting agent was HNO3 (0.2 M). In some cases, the metals were not removed fully from the used beads during the first five cycles of regeneration and reuse. The results of this investigation show that these beads are efficient adsorbents for the removal of metal ions from spiked well water samples.

Tannin complexation with metal ions and its implication on human health, environment and industry: An overview

Tannins, also known as plant polyphenols (PPs), are secondary metabolites widely existing in higher plants and are a kind of natural renewable resource with wide distribution, variety and quantity. Tannin has become an important class of fine chemicals due to the easily modified molecular structure and the properties of antibacterial and antioxidant, combining with protein and complexing with metal ion. Besides being used for tanning leather, tannins are also widely used in wood adhesive, concrete water-reducing agents, oil drilling fluid viscosity-reducing agents, pharmaceutical, mineral processing, water treatment, gas desulfurization, metal anticorrosion, wood anticorrosion, printing and dyeing, liquor clarification, oil antioxidant, daily chemical products and other products preparation. There are two groups of tannins: condensed tannins (CTs) (flavonoid-derived proanthocyanidins) and hydrolysable tannins (HTs) (gallic acid ester-derived). Tannins can form complexes with metals through the ortho-dihydroxyphenolic group(s), especially with transition metals. The structure-activity relationships, stoichiometry, and origin of the insolubility of which were emphasized. Furthermore, this paper proposed an in-depth discussion of the associations of tannins-metal complexes in human health, environment and industries.

Nanocellulose-based tannin-immobilized biosorbent for efficient copper ion removal

Tannins, which are water-soluble polyhydroxyphenols found in plant structures, offer a sustainable alternative to inorganic products for treating effluents. To overcome their solubility in water, new methods have been developed to immobilize tannin on materials such as nanocellulose, resulting in tannin-based adsorbents. This study investigates the production of different types of tannin-based adsorbents immobilized on nanocellulose nanofibrils using glutaraldehyde as a crosslinking agent. The adsorbents were characterized for their morphology, chemical composition, tannin leaching, thermal stability, and copper adsorption capacity. The main results showed that tannin leaching from the adsorbents in water was greatly reduced with glutaraldehyde. Scanning electron microscopy images showed tannin coating on the surface of nanocellulose nanofibrils due to immobilization. The lyophilized adsorbent was effective in adsorbing Cu (II) within 1 min, with the adsorbed amount increasing gradually until stabilization after 45 min. Overall, this study suggests that tannin immobilized on nanofibrillated cellulose has the potential to offer a sustainable and renewable alternative for effluent treatment.

Enhanced synergistic removal of Cu(II) and Cr(VI) with multifunctional biomass hydrogel from strong-acid media

Simultaneous recovery of heavy metal ions (HMIs) such as Cu(II) and Cr(VI) from strong-acid media was a great challenge due to the inhibition of protons. Herein, a novel biomass hydrogel (CMC/PEI-PD) containing various groups (bis-picolylamine, amino, and hydroxyl groups) was newly prepared by a facile two-step process. The static experiments relating pH, kinetics and isothermal co-adsorption confirmed the synergistic effect towards Cu(II) and Cr(VI) consistently. Specifically, the adsorption capacities of Cu(II) and Cr(VI) at pH 2.0 increased by 23.73% and 40.18% in comparison with the single systems. Moreover, coexistence of inorganic anions and cations could further increase the adsorption of Cu(II) and Cr(VI) by 59.90% and 43.39%, respectively. At the same time, the adsorption and desorption ratios for both HMIs remained stable. The superior performance came from the two dominant mechanisms of co-removal. On the one hand, Cu(II) chelated by bis-picolylamine group attracted Cr(VI) in the form of cation bridge, thus promoting Cr(VI) adsorption. On the other hand, the protonated amine group attracted Cr(VI) by electrostatic interaction and weakened the inter-cationic repulsion by electrostatic shielding, thus promoting Cu(II) adsorption. In addition, the dynamic column experiment towards simulated acidic electroplating wastewater involving Cu(II)-Cr(VI)-Ni(II) certified the high efficiency and feasibility of the co-removal. Therefore, CMC/PEI-PD owned great potential in the separation of typical HMIs even directly from strong-acid media.

Sustainable Tannin Gels for the Efficient Removal of Metal Ions and Organic Dyes

The usage of a highly efficient, low-cost, and sustainable adsorbent material as an industrial wastewater treatment technique is required. Herein, the usage of the novel, fully sustainable tannin-5-(hydroxymethyl)furfural (TH) aerogels, generated via a water-based sol-gel process, as compatible biosorbent materials is presented. In particular, this study focusses on the surface modification of the tannin biosorbent with carboxyl or amino functional groups, which, hence, alters the accessible adsorption sites, resulting in increased adsorption capacity, as well as investigating the optimal pH conditions for the adsorption process. Precisely, highest adsorption capacities are acquired for the metal cations and cationic dye in an alkaline aqueous environment using a carboxyl-functionalized tannin biosorbent, whereas the anionic dye requires an acidic environment using an amino-functionalized tannin biosorbent. Under these determined optimal conditions, the maximum monolayer adsorption capacity of the tannin biosorbent ensues in the following order: Cu2+ > RB > Zn2+ > MO, with 500, 244, 192, 131 mg g-1, respectively, indicating comparable or even superior adsorption capacities compared to conventional activated carbons or silica adsorbents. Thus, these functionalized, fully sustainable, inexpensive tannin biosorbent materials, that feature high porosity and high specific surface areas, are ideal industrial candidates for the versatile adsorption process from contaminated (heavy) metal or dye solutions.

Synthesis of magnetic sodium lignosulfonate hydrogel(Fe3O4@LS) and its adsorption behavior for Cd2+ in wastewater

Heavy metal pollution is becoming increasingly serious. Heavy metal pollutants are nonbiodegradable and can be bioenriched through the food chain, and thus, they greatly threaten the environment and human health. Hydrogels, as an ideal adsorbent, have been widely used to treat heavy metal industrial wastewater. Sodium lignosulfonate hydrogel (LS) was prepared by free-radical grafting copolymerization, and nano-Fe3O4 particles were loaded in LS by an in-situ precipitation method (Fe3O4@LS). The magnetic properties and adsorption capacity of Fe3O4@LS are closely related to the load capacity of Fe3O4. XRD, FTIR, XPS, SEM, TEM, BET, and TGA analyses of the materials were performed. Subsequently, the removal effect of the typical pollutant Cd2+ in heavy metal-polluted water was studied with Fe3O4@LS as the adsorbent. The influences of the Fe3O4@LS dosage and initial pH were investigated, and the adsorption kinetics and thermodynamics were further explored and discussed. Finally, the adsorption mechanism of Fe3O4@LS on Cd2+ was obtained. Results show that Fe3O4@LS has a more stable spatial network structure than LS, and the pore size, specific surface area and active sites increase. The maximum adsorption capacity can reach 88.00 mg/g when pH = 6 and the dosage of Fe3O4@LS is 1000 mg/L. The adsorption of Cd2+ by Fe3O4@LS conforms to pseudosecond-order kinetics and the Temkin isothermal adsorption model. Further mechanistic investigations show that the sorption of Cd2+ on Fe3O4@LS is mainly attributed to surface complexation, electrostatic attraction and coprecipitation. The coexistence of cations in water will inhibit the adsorption of Fe3O4@LS. Fe3O4@LS has superparamagnetism and a good response to an external magnetic field. The adsorption rate can still reach >60 % after four elutions with NaCl as the eluent. This material can be reused and has good application potential.

Harnessing Nature's Ingenuity: A Comprehensive Exploration of Nanocellulose from Production to Cutting-Edge Applications in Engineering and Sciences

Primary material supply is the heart of engineering and sciences. The depletion of natural resources and an increase in the human population by a billion in 13 to 15 years pose a critical concern regarding the sustainability of these materials; therefore, functionalizing renewable materials, such as nanocellulose, by possibly exploiting their properties for various practical applications, has been undertaken worldwide. Nanocellulose has emerged as a dominant green natural material with attractive and tailorable physicochemical properties, is renewable and sustainable, and shows biocompatibility and tunable surface properties. Nanocellulose is derived from cellulose, the most abundant polymer in nature with the remarkable properties of nanomaterials. This article provides a comprehensive overview of the methods used for nanocellulose preparation, structure-property and structure-property correlations, and the application of nanocellulose and its nanocomposite materials. This article differentiates the classification of nanocellulose, provides a brief account of the production methods that have been developed for isolating nanocellulose, highlights a range of unique properties of nanocellulose that have been extracted from different kinds of experiments and studies, and elaborates on nanocellulose potential applications in various areas. The present review is anticipated to provide the readers with the progress and knowledge related to nanocellulose. Pushing the boundaries of nanocellulose further into cutting-edge applications will be of particular interest in the future, especially as cost-effective commercial sources of nanocellulose continue to emerge.

Highly Efficient Cationic/Anionic Cellulose Membranes for Removal of Cr(VI) and Pb(II) Ions

To achieve high throughput, low-pressure drops, and high adsorption capacity of Cr(VI) and Pb(II) in industrial wastewater treatment, cellulose membranes containing cationic and anionic groups were fabricated, respectively. In this process, cost-effective cotton fabrics were oxidized using sodium periodate, followed by quaternary ammonium or sulfonation modifications. The chemical composition, surface morphology, and thermal and mechanical properties of the cellulose membranes were investigated by ATR-FTIR, solid-state NMR, SEM, TGA, and tensile experiments. Quaternary ammonium, aldehyde, and sulfonate groups were distributed on the cationic/anionic cellulose fibers as adsorption sites, which issue remarkable adsorption capability to the cellulose membranes. The highly toxic Cr(VI) and Pb(II) ions were used to challenge the adsorption capacity of the cationic and anionic cellulose membranes, respectively. The maximum adsorption capacities of Cr(VI) and Pb(II) ions were 61.7 and 63.7 mg/g, respectively, suggested by Langmuir isotherms, kinetics, and thermodynamics in the static experiments. The dynamic adsorption capability of cationic cellulose membranes against Cr(VI) ions was determined and compared with that of commercially available anionic-exchange membranes. Spiral wound filtration cartridges were fabricated by cationic and anionic cellulose membranes, respectively, and were used to adsorb Cr(VI) and Pb(II) from lab-made wastewater, respectively. The cationic cellulose cartridge can purify 4.4 L of wastewater containing 1.0 mg/L of Cr(VI) ions with a 100% removal ratio, while the pressure drop was retained at 246 Pa. Similarly, the anionic cellulose cartridge exhibited even more impressive adsorption capability; the removal ratio against Pb(II) was 99% when 8.6 L of 1.0 mg/L of Pb(II) ions containing wastewater was treated, and the pressure drop was retained at 234 Pa. A composite cartridge fabricated by the integration of cationic and anionic cellulose membranes was successfully employed to purify the wastewater containing Cr(VI) and Pb(II) simultaneously. The possible adsorption mechanism was proposed, and the recycling ability of the cellulose membranes was also discussed.

Nanocellulose-based aerogels for water purification: A review

Water purification using thin membranes at high pressures through adsorption and size exclusion is the widely used mechanism due to its simplicity and enhanced efficiency compared to other traditional water purification methods. Aerogels have the potential to replace conventional thin membranes considering their unmatched adsorption/absorption capacity and higher water flux due to their unique highly porous (99 %) 3D structure, ultra-low density (~1.1 to 500 mg/cm³), and very high surface area. The availability of a large number of functional groups, surface tunability, hydrophilicity, tensile strength and flexibility of nanocellulose (NC) makes it a potential candidate for aerogel preparation. This review discusses the preparation and employment of NC-based aerogels in the removal of dyes, metal ions and oils/organic solvents. It also offers recent updates on the effect of various parameters that enhance its adsorption/absorption performance. The future perspectives of NC aerogels and their performance with the emerging materials chitosan and graphene oxide are also compared.

Preparation of sludge-cyanobacteria composite carbon for synergistically enhanced co-removal of Cu(II) and Cr(VI)

Traditional sludge disposal is currently restricted by the risk of secondary pollution. Sludge carbon material has gained widespread attention because of its low cost and environmentally sustainable properties. However, owing to the high ash content and low-energy density of sludge, sludge pyrolysis alone has certain limitations, and the performance of carbon materials needs to be improved. Herein, a sludge-cyanobacteria composite carbon (SCC) was easily synthesized, and the adsorption process of Cu(II) and Cr(VI) by SCC was examined. SCC-700-2-50% exhibited a high S_BET (1047.54 m²/g) and developed pore structure rich in functional groups (such as -NH, -OH, and C-O). The combination of pore structure and functional groups improved the adsorption performance of SCC. The adsorption processes exhibited a synergistic effect in a binary system: the q_m of Cu(II) and Cr(VI) were 386 mg/g and 341 mg/g, respectively, and the selectivity of Cu(II) adsorption by SCC was greater than Cr(VI). The adsorption process, examined by SEM-EDS, FTIR, and XPS analysis, indicated that Cu(II) as a cationic interface strengthens Cr(VI) adsorption through electrostatic interaction, and the anion Cr(VI) created a valid electrostatic shield against the electrostatic repulsion between H⁺ and Cu(II), facilitating Cu(II) adsorption. SCC had great reusability: Cu(II) and Cr(VI) adsorption capacity were 90% and 84%, of the initial adsorption capacity, respectively, after six cycles. This study demonstrates the prospect of SCC as a valid adsorbent for multiple heavy metal contaminations removal.

Immobilization of tannin onto dialdehyde chitosan as a strategy for highly efficient and selective Au(III) adsorption

Recycling of Au(III) from wastewater can not only increase resource utilization but also reduce environmental pollution. Herein, a chitosan-based bio-adsorbent (DCTS-TA) was successfully synthesized via crosslinking reaction between tannin (TA) and dialdehyde chitosan (DCTS) for the recovery of Au(III) from the solution. The maximum adsorption capacity for Au(III) was 1146.59 mg/g at pH 3.0, which fitted well with the Langmuir model. The XRD, XPS, and SEM-EDS analyses demonstrated that Au(III) adsorption on DCTS-TA was a collaborative process involving electrostatic interaction, chelation, and redox reaction. Existence of multiple coexisting metal ions did not significantly affect the Au(III) adsorption efficiency, with >90 % recovery of DCTS-TA obtained after five cycles. DCTS-TA is a promising candidate for Au(III) recovery from aqueous solutions due to its easy preparation, environmental-friendliness, and high efficiency.

Sodium humate based double network hydrogel for Cu and Pb removal

Sodium humate (SH) is one of the derivatives humic substances, which can be utilized for heavy metal removal from water due to its containing plenty of functional groups. In this study, a double network hydrogel SH/polyacrylamide (SH/PAM) was synthesized by a simple free-radical polymerization and used for Cu²⁺ and Pb²⁺ removal from water. The adsorption process can be well described by Langmuir-Freundlich model, indicating that both physical and chemical adsorption were involved. X-ray photoelectron spectroscopy (XPS) characterization demonstrated that complexation was the main mechanism for the adsorption. Two-dimensional correlation analysis of FTIR (2D-FTIR-COS) results showed that the variation order of functional groups during Cu²⁺ and Pb²⁺ adsorption in the following order: COOH ≈ -CO > -OH > C-O and -COOH ≈ C-O > -CO > -OH, respectively. According to the density functional theory (DFT) calculation results, the O atom of SH in the COO^- was the main adsorption site. Meanwhile, the adsorption energy of Pb²⁺ was more negative than that of Cu²⁺ and the orbital hybridization between O atom of SH and Pb²⁺ was denser than that of Cu²⁺, which suggested that SH/PAM had a stronger combining capacity for Pb²⁺ than Cu²⁺. Therefore, the adsorption capacity for Pb²⁺ was larger than Cu²⁺. Moreover, the removal efficiencies are 30.2% for Al, 98.79% for Cu, 99.0% for Fe, 17.2% for Mn, 93.4% for Pb, and 62.4% for Zn in actual acid mine drainage using 6 g L^-1 adsorbent. Collectively, this study not only provided a new adsorbent for heavy metal removal but also explicated the mechanism of heavy metal removal by SH from molecule and electron perspective, which is helpful for the application of SH in the environmental field.

Hexavalent Chromium Removal from Industrial Wastewater by Adsorption and Reduction onto Cationic Cellulose Nanocrystals

Cationic cellulose nanocrystals (CCNC) are lignocellulosic bio-nanomaterials that present large, specific areas rich with active surface cationic groups. This study shows the adsorption removal of hexavalent chromium (Cr(VI)) from industrial wastewaters by the CCNC. The CCNC were synthetized through periodate oxidation and Girard's reagent-T cationization. The high value of CCNCs cationic groups and anionic demand reveal probable nanocrystal-Cr(VI) attraction. Adsorption was performed with synthetic Cr(VI) water at different pH, dosage, Cr(VI) concentration and temperature. Fast removal of Cr(VI) was found while operating at pH 3 and 100 mg·L^-1 of dosage. Nevertheless, a first slower complete removal of chromium was achieved by a lower CCNC dosage (40 mg·L^-1). Cr(VI) was fully converted by CCNC into less-toxic trivalent species, kept mainly attached to the material surface. The maximum adsorption capacity was 44 mg·g^-1. Two mechanisms were found for low chromium concentrations (Pseudo-first and pseudo-second kinetic models and continuous growth multi-step intraparticle) and for high concentrations (Elovich model and sequential fast growth-plateau-slow growth intraparticle steps). The Sips model was the best-fitting isotherm. Isotherm thermodynamic analysis indicated a dominant physical sorption. The Arrhenius equation revealed an activation energy between physical and chemical adsorption. CCNC application at selected conditions in industrial wastewater achieved a legal discharge limit of 40 min.

Comparing the influence of humic/fulvic acid and tannic acid on Cr(VI) adsorption onto polystyrene microplastics: Evidence for the formation of Cr(OH)3 colloids

Microplastics (MPs) can act as vectors for various contaminants in the aquatic environment. Although some research has investigated the adsorption characteristics and influencing factors of metals/organic molecules on MPs, the effects of dissolved organic matter (DOM) (which are ubiquitous active species in ecosystems) on metal oxyanions such as Cr(VI) capture by MPs are largely unknown. This study explored the adsorption behaviors and mechanisms of Cr(VI) oxyanions onto polystyrene (PS) MPs using batch adsorption experiments and multiple spectroscopic methods. The effects of representative DOM components (i.e., humic acid (HA), fulvic acid (FA) and tannic acid (TA)) on Cr(VI) capture by PS were particularly studied. Results revealed a significantly enhanced adsorption of Cr(VI) on PS in the presence of TA. The Cr(VI) adsorption capacity was increased from 2876 μg g^-1 to 4259 μg g^-1 and 5135 μg g^-1 when the TA concentrations raised from 0 to 10 and 20 mg L^-1, respectively. Combined microscopic and spectroscopic investigations revealed that Cr(VI) was reduced to Cr(III) by TA and formed stable Cr(OH)₃ colloids on PS surfaces. Contrarily, HA and FA inhibited Cr(VI) adsorption onto PS, especially at pH > 2.0 and higher DOM concentrations, due to site competition and electrostatic repulsion. Increase in pH was found to reduce zeta potentials of MPs, resulting in inhibited Cr(VI) adsorption. The adsorbed Cr(VI) declined with increasing ionic strength, implying that outer-sphere surface complexation affected the adsorption process in the presence of DOM. These new findings improved our fundamental understanding of the fate of Cr(VI) and MPs in DOM-rich environmental matrices.

The synthesis of nanocellulose-based nanocomposites for the effective removal of hexavalent chromium ions from aqueous solution

The present study reports the synthesis of a polydopamine (PDA)/nanocellulose (NC) nanocomposite for the effective removal of chromium ions from water. PDA was used to modify NC surface producing a nanocomposite namely PDA/NC, by in situ polymerization of dopamine on the surface of NC. Thereafter, the as-synthesized nanocomposite was characterized using familiar techniques such as Fourier transform infrared, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, and transmission electron microscopy. All results indicated the successful combination of PDA and NC in one nanocomposite. The PDA/NC nanocomposite was evaluated for the removal of hexavalent Cr(vi) ions from an aqueous solution. The adsorption conditions, such as pH, contact time, and initial Cr(vi) concentration, were optimized. Adsorption kinetic studies revealed that Cr(vi) removal on the surface of PDA/NC nanocomposite followed the pseudo-second-order kinetic model. Furthermore, isotherm studies revealed that Cr(vi) removal followed the Langmuir isotherm model with a maximum adsorption capacity (q m) of 210 mg/g. The adsorption mechanism study indicated that the Cr(vi) removal was reached via complexation, adsorption, and chemical reduction. The reusability of a PDA/NC nanocomposite for the removal of Cr(vi) ions was studied up to five cycles with acceptable results. The high adsorption capacity and multiple removal mechanisms validated the effective applicability of PDA/NC nanocomposite as a useful adsorbent for the removal of Cr(vi) ions from aqueous solution.

Recent Advances in Designing Fibrous Biomaterials for the Domain of Biomedical, Clinical, and Environmental Applications

Unique properties and potential applications of nanofibers have emerged as innovative approaches and opportunities in the biomedical, healthcare, environmental, and biosensor fields. Electrospinning and centrifugal spinning strategies have gained considerable attention among all kinds of strategies to produce nanofibers. These techniques produce nanofibers with high porosity and surface area, adequate pore architecture, and diverse chemical compositions. The extraordinary characteristics of nanofibers have unveiled new gates in nanomedicine to establish innovative fiber-based formulations for biomedical use, healthcare, and a wide range of other applications. The present review aims to provide a comprehensive overview of nanofibers and their broad range of applications, including drug delivery, biomedical scaffolds, tissue/bone-tissue engineering, dental applications, and environmental remediation in a single place. The review begins with a brief introduction followed by potential applications of nanofibers. Finally, the future perspectives and current challenges of nanofibers are demonstrated. This review will help researchers to engineer more efficient multifunctional nanofibers with improved characteristics for their effective use in broad areas. We strongly believe this review is a reader's delight and will help in dealing with the fundamental principles and applications of nanofiber-based scaffolds. This review will assist students and a broad range of scientific communities to understand the significance of nanofibers in several domains of nanotechnology, nanomedicine, biotechnology, and environmental remediation, which will set a benchmark for further research.

Modeling of Hexavalent Chromium Removal with Hydrophobically Modified Cellulose Nanofibers

Cellulose nanofibers (CNF) are sustainable nanomaterials, obtained by the mechanical disintegration of cellulose, whose properties make them an interesting adsorbent material due to their high specific area and active groups. CNF are easily functionalized to optimize the performance for different uses. The hypothesis of this work is that hydrophobization can be used to improve their ability as adsorbents. Therefore, hydrophobic CNF was applied to adsorb hexavalent chromium from wastewater. CNF was synthetized by TEMPO-mediated oxidation, followed by mechanical disintegration. Hydrophobization was performed using methyl trimetoxysilane (MTMS) as a hydrophobic coating agent. The adsorption treatment of hexavalent chromium with hydrophobic CNF was optimized by studying the influence of contact time, MTMS dosage (0-3 mmol·g^-1 CNF), initial pH of the wastewater (3-9), initial chromium concentration (0.10-50 mg·L^-1), and adsorbent dosage (250-1000 mg CNF·L^-1). Furthermore, the corresponding adsorption mechanism was identified. Complete adsorption of hexavalent chromium was achieved with CNF hydrophobized with 1.5 mmol MTMS·g^-1 CNF with the faster adsorption kinetic, which proved the initial hypothesis that hydrophobic CNF improves the adsorption capacity of hydrophilic CNF. The optimal adsorption conditions were pH 3 and the adsorbent dosage was over 500 mg·L^-1. The maximum removal was found for the initial concentrations of hexavalent chromium below 1 mg·L^-1 and a maximum adsorption capacity of 70.38 mg·g^-1 was achieved. The kinetic study revealed that pseudo-second order kinetics was the best fitting model at a low concentration while the intraparticle diffusion model fit better for higher concentrations, describing a multi-step mechanism of hexavalent chromium onto the adsorbent surface. The Freundlich isotherm was the best adjustment model.

Tannin-based coagulants: Current development and prospects on synthesis and uses

Population growth, industrialization, urbanization, and agriculture lead to a decrease in the availability of clean water. Coagulation/flocculation is one of the most common operations in water, urban wastewater, and industrial effluents treatment systems. Usually, this process is achieved using conventional coagulants that have their performance affected by pH, are poorly biodegradable, produce a huge volume of sludge, and are associated with degenerative diseases. As a substitute for these chemicals, natural coagulants have been highly researched for the last ten/fifteen years, especially the tannin-based (TB) ones. This review paper highlights the advantages of using these greener products to treat different types of water, wastewater, and effluents, especially from dairy, cosmetics, laundries, textile, and other industries. TB coagulants can successfully remove turbidity, color, suspended solids, soluble organic (chemical/biochemical oxygen demand) and inorganic matter (total phosphate, and heavy metals), and microorganisms. TB coagulants are compatible with other treatment technologies and can be used as coagulant-aid to reduce the consumption of chemicals. TB coagulants can reduce operating costs of water treatment due to less alkalinity consumption, as pH adjustment is sometimes unnecessary, and the production of a smaller volume of biodegradable sludge. TB coagulants can be synthesized by valorizing wastes/by-products, from the bark of some specific trees and skins/pomace of different fruits and vegetables. The strengths, weaknesses, opportunities, and threats (SWOT) on TB coagulants are discussed. The progress of TB coagulants is promising, but some threats should be overcome, especially on tannin extraction and cationization. The market competition with conventional coagulants, the feasibility of application in real waters, and the reluctance of the industries to adapt to new technologies are other weaknesses to be surpassed.

Preparation and characterization of cellulose nanocrystals from spent edible fungus substrate

BACKGROUND

Spent edible fungus substrates were identified as potential sources to produce cellulose derivatives, namely purified cellulose and dicarboxyl cellulose nanocrystal (DCNC). Purified celluloses were obtained via chemical treatments and then oxidized by sequential periodate-chlorite without mechanical process. The structural properties of the DCNCs were characterized by transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermal gravimetric analysis (TGA).

RESULTS

XRD results showed that the cellulose I structure was maintained, however, the crystallinity index decreased after oxidation process. The initial pyrolysis temperature of DCNCs ranged from 242 to 344 °C. TEM results revealed that DCNC was rod-shaped with an average length and width of 130.88 nm and 7.3 nm, respectively. The average specific surface area (SSA) was 366.67 m²  g^-1 . The carboxyl content was around 3.485 mmol g^-1 . Finally, the adsorption capacity for contaminations was 76.98, 126.22, 64.44 and 9.63 mg g^-1 for copper ion (Cu²⁺ ), lead ion (Pb²⁺ ), chromium (Cr³⁺ ) and amoxicillin (AMX), respectively.

CONCLUSION

This work showed a sequentially chemical oxidation for preparing nanocellulose from secondary agricultural waste with many functional applications. © 2021 Society of Chemical Industry.

Removal of Hg2+ from desulfurization wastewater by tannin-immobilized graphene oxide

A novel adsorbent consisting of tannic acid (TA) immobilized on graphene oxide (GO) was proposed and used to remove Hg²⁺ from desulfurization wastewater. The morphology and physicochemical properties of tannin-immobilized graphene oxide (TAIGO) were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The characterization results showed that TA was successfully immobilized on GO, and that new functional groups were introduced on TAIGO. The effects of contact time, adsorbent dose, pH, and ion components on removal efficiency were evaluated. The adsorption process was found to be complete within 15 min, and the removal efficiency increased with increasing adsorbent dosage. The pH value affected the protonation of TAIGO and the form of Hg²⁺ in wastewater. High concentrations of Cl^- and SO₃^2- hindered the adsorption performance, whereas SO₄^2- and cations had a negligible effect. In addition, the excellent economic benefits of TAIGO were analyzed in an economic evaluation, and the Hg²⁺ removal efficiency remained at 88% after three recycles. A pseudo-second-order kinetic model (R = 0.9995) was used to fit the adsorption process, and the oxygen-containing functional groups and chelation reaction played critical roles in adsorption. TAIGO is a low-cost adsorbent with high Hg²⁺ removal efficiency and could be further used in practical desulfurization wastewater.

A review on three-dimensional cellulose-based aerogels for the removal of heavy metals from water

Contamination of the aquatic ecosystem by heavy metals is a growing concern that has yet to be addressed with an efficient, cost-effective and environmentally-friendly solution. Heavy metals occur naturally in the earth's crust and also result from anthropogenic activities. Due to the rapid increase in industrialization, there is an increase in consumer demands across various industries such as metal processing, mining sector, agricultural activities, etc. and this has led to an increase in heavy metal concentrations in the aqueous environment. Cellulose-based aerogels are a novel third-generation of aerogels that have recently attracted a lot of attention due to their high adsorption efficiency, eco-friendly prospects and cost effectiveness. In this review, recent literature on cellulose-based aerogel adsorbents used for the removal of heavy metals from aqueous solution has been compiled. The preparation of cellulose-based aerogels, adsorption mechanisms, effects of experimental factors such as pH, temperature, contact time, initial metal concentration and adsorbent dose have been discussed. In addition, cost analysis of cellulose-based adsorbents and some challenges in this research field along with recommendations of improvements have been presented. It can be concluded that functionalizing of cellulose-based aerogels with amine groups, thiol groups, other compounds such as nanobentonite and chitosan results in very high adsorption capacities. The adsorption studies revealed that pseudo-second-order kinetic model was the most commonly encountered adsorption kinetic model, and the most commonly encountered adsorption isotherm model was the Langmuir isotherm model. The main adsorption mechanisms were electrostatic interaction, complexation and ion exchange.

Magnetic polyphenol nanocomposite of Fe3O4/SiO2/PP for Cd(II) adsorption from aqueous solution

In order to solve the water solubility and difficult re-use of plant polyphenol (PP) in Cd(II) adsorption, PP was immobilized on the surface of magnetic material in this study. A core-shell nanocomposite Fe₃O₄/SiO₂/PP (∼18 nm) was synthesized with 3-8 nm SiO₂ and 2-5 nm PP. TGA analysis revealed the PP coating amount was 2.39%. VSM detection suggested that saturation magnetization of Fe₃O₄/SiO₂/PP was 45.94 emu/g. The adsorption equilibrium was reached in 2 h and the adsorption kinetics followed a pseudo-second-order model. The adsorption data fitted well to a Langmuir isotherm, achieving a 98.6% of Cd(II) removal at 0.6 g, pH 7.0, 298 K and 160 rpm. The adsorption capacity of Cd(II) on Fe₃O₄/SiO₂/PP highly depended on the pH. The adsorption capacity increased as the initial solution pH was increased in the range of 3.0-8.0. The adsorbed Cd(II) on Fe₃O₄/SiO₂/PP could be effectively desorbed by 0.1 mol/L of HNO₃ and the Fe₃O₄/SiO₂/PP still maintained a stable adsorption capacity after five cycles. The adsorption mechanism of Cd(II) on Fe₃O₄/SiO₂/PP is mainly dependent on complexation and electrostatic adsorption from the FTIR and XPS analyses. This study provided a new way for PP to remove Cd(II) from aqueous solution.

Insights into selective adsorption mechanism of copper and zinc ions onto biogas residue-based adsorbent: Theoretical calculation and electronegativity difference

Modified biomass-based adsorption technique has attracted much attention in heavy metal ions removal, but selective adsorption behavior and mechanism of heavy metal ions adsorption onto biosorbent still need to be further clarified. Herein, a carboxylated biogas residue (BR-COOH) was prepared to remove the Cu²⁺ and Zn²⁺ from single/binary heavy metal ions solution and explore selective adsorption mechanism. The results exhibited that the adsorption capacities of BR-COOH for Cu²⁺ was higher than that for Zn²⁺ obviously, whether in the single or binary heavy metal ions solution. Meanwhile, the introduced carboxy groups were identified as the main sites for metal ions adsorption. Density functional theory (DFT) calculation results exhibited that the adsorption energy of Cu²⁺ (-0.51 eV) onto BR-COOH was lower than that of Zn²⁺ (-0.47 eV), indicating that the Cu²⁺ adsorbed on BR-COOH was more stable than Zn²⁺. Moreover, the metal ions adsorption capacity of BR-COOH was positively correlated with their electronegativity, which was due to that the metal ions with stronger electronegativity was more easily interacted with the negatively charged oxygen in carboxyl groups. The same results were also verified in the control experiment conducted with two other biosorbents. Therefore, the work provided a new and in-depth insight into selective adsorption of metal ions onto carboxylated biosorbent.

Highly efficient and rapid Pb(ii) removal from acidic wastewater using superhydrophilic polystyrene phosphate resin

Novel superhydrophilic polystyrene phosphate resin was synthesized for efficient and rapid Pb(ii) removal from acidic wastewater.

Preparation of MES@Fe3O4@SiO2-PPy magnetic microspheres for the highly efficient removal of Cr(vi)

A novel magnetic adsorbent, PPy-modified silica-coated magnetic MES organic–inorganic composite (MFSP), with high dispersibility, abundant adsorption sites, and magnetic separation was prepared successfully for the adsorption or reduction of Cr(vi).

Preparation of a Novel Activated Carbon from Cassava Sludge for the High-Efficiency Adsorption of Hexavalent Chromium in Potable Water: Adsorption Performance and Mechanism Insight

Particularly, because of the leakage risk of metal elements from sludge carbon, little attention has been focused on using sludge activated carbon as an adsorbent for the removal of Cr (VI) from contaminated water sources. Herein, a novel sludge carbon derived from dewatered cassava sludge was synthesized by pyrolysis using ZnCl2 as an activator at the optimal conditions. The prepared sludge activated carbon possessed a large BET surface (509.03 m2/g), demonstrating an efficient removal for Cr (VI). Although the time to reach equilibrium was extended by increasing the initial Cr (VI) concentration, the adsorption process was completed within 3 h. The kinetics of adsorption agreed with the Elovich model. The whole adsorption rate was controlled by both film and intra-particle diffusion. The Cr (VI) removal efficiency increased with elevating temperature, and the adsorption equilibrium process followed the Freundlich isotherm model. The adsorption occurred spontaneously with endothermic nature. The removal mechanism of Cr (VI) on the prepared sludge activated carbon depended highly on solution pH, involving pore filling, electrostatic attraction, reduction, and ion exchange. The trace leakage of metal elements after use was confirmed. Therefore, the prepared sludge activated carbon was considered to be a highly potential adsorbent for Cr (VI) removal from contaminated raw water.

Heavy Metal Adsorption Using Magnetic Nanoparticles for Water Purification: A Critical Review

Research on contamination of groundwater and drinking water is of major importance. Due to the rapid and significant progress in the last decade in nanotechnology and its potential applications to water purification, such as adsorption of heavy metal ion from contaminated water, a wide number of articles have been published. An evaluating frame of the main findings of recent research on heavy metal removal using magnetic nanoparticles, with emphasis on water quality and method applicability, is presented. A large number of articles have been studied with a focus on the synthesis and characterization procedures for bare and modified magnetic nanoparticles as well as on their adsorption capacity and the corresponding desorption process of the methods are presented. The present review analysis shows that the experimental procedures demonstrate high adsorption capacity for pollutants from aquatic solutions. Moreover, reuse of the employed nanoparticles up to five times leads to an efficiency up to 90%. We must mention also that in some rare occasions, nanoparticles have been reused up to 22 times.

Enhancing Removal of Cr(VI), Pb2+, and Cu2+ from Aqueous Solutions Using Amino-Functionalized Cellulose Nanocrystal

In this work, the amino-functionalized cellulose nanocrystal (ACNC) was prepared using a green route and applied as a biosorbent for adsorption of Cr(VI), Pb²⁺, and Cu²⁺ from aqueous solutions. CNC was firstly oxidized by sodium periodate to yield the dialdehyde nanocellulose (DACNC). Then, DACNC reacted with diethylenetriamine (DETA) to obtain amino-functionalized nanocellulose (ACNC) through a Schiff base reaction. The properties of DACNC and ACNC were characterized by using elemental analysis, Fourier transform infrared spectroscopy (FT-IR), Kaiser test, atomic force microscopy (AFM), X-ray diffraction (XRD), and zeta potential measurement. The presence of free amino groups was evidenced by the FT-IR results and Kaiser test. ACNCs exhibited an amphoteric nature with isoelectric points between pH 8 and 9. After the chemical modification, the cellulose I polymorph of nanocellulose remained, while the crystallinity decreased. The adsorption behavior of ACNC was investigated for the removal of Cr(VI), Pb²⁺, and Cu²⁺ in aqueous solutions. The maximum adsorption capacities were obtained at pH 2 for Cr(VI) and pH 6 for Cu²⁺ and Pb²⁺, respectively. The adsorption all followed pseudo second-order kinetics and Sips adsorption isotherms. The estimated adsorption capacities for Cr(VI), Pb²⁺, and Cu²⁺ were 70.503, 54.115, and 49.600 mg/g, respectively.

Migration of leather tannins and chromium in soils under the effect of simulated rain

Chromium (Cr) and tannin are two major pollutants in leather industry. However, little is known about the co-migration of leather tannins and Cr in soils. In this study, column experiments were conducted to estimate Cr leaching behavior from topsoil and the environmental risk of the leachate at various tannin dosages and different ways (tannin either directly adding to the Cr-contaminated soil or adding stepwise through simulated rain) into the soil. The total Cr concentration in leachate was positively related with tannin content in soil, while Cr (Ⅵ) concentration was negatively correlated. The maximum cumulative leaching efficiency of total Cr from soil after six leaching events was 44.65% with 3 mg/g tannin adding into soil directly, and the maximum cumulative leaching efficiency of Cr (Ⅵ) was 38.75% with simulated rain leaching Cr-contaminated soil. With 3 mg/g tannin adding into soil, tannin concentration in the top layer (0-7 cm) lost by 32.67% after leaching, the amount of decomposed tannin was 0.25 mg/g, excluding the amount of tannin in leachate (3.63 mg/L) and the original amount in the soil (0.34 mg/g), indicating a slow degradation under natural condition. Both of the total Cr and Cr (Ⅵ) concentration in each layer of the soil columns decreased under tannin treatments compared with control. Compared with tannin adding stepwise into simulated rain, adding tannin into soil significantly (p < 0.05) affected the migration of Cr. Tannin increased the residual fraction while decreased the exchangeable fraction of Cr in the soils. Overall, this research can provide reference information for environmental risk assessment of contaminants in tanning sites.

Advances in nanocellulose-based materials as adsorbents of heavy metals and dyes

In recent years, nanocellulose-based materials have been increasingly applied as a lot of biosorbents for the treatment of water pollutants due to their large specific surface area, easy modification, environmental friendliness, and reproducibility. In this review, surface modification of nanocellulose-based adsorbents with various effective adsorption groups is described, as well as polymer grafting and hybrid composite fabrication. The adsorption mechanisms involved in the adsorption process of pollutants by adsorbents are further analysed and summarized. The regeneration methods of nanocellulose adsorbents with different adsorption mechanisms are also demonstrated. In addition, this paper also briefly describes the forms of nanocellulose-based adsorbents with large-scale application including membranes, gels, flocculants and magnetic composites.

Efficient Removal of Pb(II) from Aqueous Systems Using Spirulina-Based Biohybrid Magnetic Helical Microrobots

Wastewater remediation toward heavy metal pollutants has attracted considerable attention, and various adsorption-based materials were employed in recent years. However, it is still challenging to explore low-cost and high-efficient adsorbents with superior removal performance, nontoxicity, flexible operation, and good reusability. Herein, Fe3O4- and MnO2-loaded biohybrid magnetic helical microrobots (BMHMs) based on Spirulina cells were presented for the first time, and their performance on Pb(II) removal was studied in detail. Intracellular synthesis of Fe3O4 and MnO2 nanoparticles into Spirulina cells was successively conducted to obtain the BMHMs with superparamagnetism and high surface activity. The BMHMs could be flexibly propelled under magnetic actuation, and collective cork-screw spinning was performed to enhance fluidic diffusion with intensive adsorption. Rapid and significant removal of Pb(II) in wastewater was achieved using the swarming microrobots, and a high adsorption capacity could be reached at 245.1 mg/g. Moreover, the BMHMs could be cyclically reutilized after simple regeneration, and good specificity toward Pb(II) was verified. The adsorption mechanism was further studied, which revealed that the pseudo-second-order kinetics dominated in the adsorption process, and the Langmuir isothermal model also fitted the experimental results well. The intriguing properties of the BMHMs enable them to be versatile platforms with significant potentials in wastewater remediation.

Synthesis of Calcium Silicate Hydrate from Coal Gangue for Cr(VI) and Cu(II) Removal from Aqueous Solution

Both the accumulation of coal gangue and potentially toxic elements in aqueous solution have caused biological damage to the surrounding ecosystem of the Huainan coal mining field. In this study, coal gangue was used to synthesize calcium silicate hydrate (C-S-H) to remove Cr(VI) and Cu(II)from aqueous solutions and aqueous solution. The optimum parameters for C-S-H synthesis were 700 °C for 1 h and a Ca/Si molar ratio of 1.0. Quantitative sorption analysis was done at variable temperature, C-S-H dosages, solution pH, initial concentrations of metals, and reaction time. The solution pH was precisely controlled by a pH meter. The adsorption temperature was controlled by a thermostatic gas bath oscillator. The error of solution temperature was controlled at ± 0.3, compared with the adsorption temperature. For Cr(VI) and Cu(II), the optimum initial concentration, temperature, and reaction time were 200 mg/L, 40 °C and 90 min, pH 2 and 0.1 g C-S-H for Cr(VI), pH 6 and 0.07 g C-S-H for Cu(II), respectively. The maximum adsorption capacities of Cr(VI) and Cu(II) were 68.03 and 70.42 mg·g⁻¹, respectively. Furthermore, the concentrations of Cu(II) and Cr(VI) in aqueous solution could meet the surface water quality standards in China. The adsorption mechanism of Cu(II) and Cr(VI) onto C-S-H were reduction, electrostatic interaction, chelation interaction, and surface complexation. It was found that C-S-H is an environmentally friendly adsorbent for effective removal of metals from aqueous solution through different mechanisms.

Potential of nanocellulose for wastewater treatment

Wastewater management has significant interest worldwide to establish viable treatment techniques to ensure the availability of clean water. The specialities of nanocellulose for this particular application is due to their high aspect ratio and accessibility of plenty of -OH groups for binding with dyes, heavy metals and other pollutants. This review aggregates the application of nanocellulose for wastewater treatment particularly as adsorbents of dyes and heavy metals, and also as membranes for filtering various other contaminants including microbes. The membrane technologies are proven to be effective relating to their durability and separation effectiveness. The commercial scale application of nanocellulose based materials in water treatment processes depend on various factors like routes of synthesis, surface modifications, hydrophilic/hydrophobic, porosity, durability etc. The recent developments on production of novel adsorbents or membranes encourage the implementation of nanocellulose based cleaner technologies for wastewater treatment.