Supramolecular Gels Based on C3-Symmetric Amides: Application in Anion-Sensing and Removal of Dyes from Water

We modified C3-symmetric benzene-1,3,5-tris-amide (BTA) by introducing flexible linkers in order to generate an N-centered BTA (N-BTA) molecule. The N-BTA compound formed gels in alcohols and aqueous mixtures of high-polar solvents. Rheological studies showed that the DMSO/water (1:1, v/v) gels were mechanically stronger compared to other gels, and a similar trend was observed for thermal stability. Powder X-ray analysis of the xerogel obtained from various aqueous gels revealed that the packing modes of the gelators in these systems were similar. The stimuli-responsive properties of the N-BTA towards sodium/potassium salts indicated that the gel network collapsed in the presence of more nucleophilic anions such as cyanide, fluoride, and chloride salts at the MGC, but the gel network was intact when in contact with nitrate, sulphate, acetate, bromide, and iodide salts, indicating the anion-responsive properties of N-BTA gels. Anion-induced gel formation was observed for less nucleophilic anions below the MGC of N-BTA. The ability of N-BTA gels to act as an adsorbent for hazardous anionic and cationic dyes in water was evaluated. The results indicated that the ethanolic gels of N-BTA successfully absorbed methylene blue and methyl orange dyes from water. This work demonstrates the potential of the N-BTA gelator to act as a stimuli-responsive material and a promising candidate for water purification.

Evaluation of the Dye Extraction Using Designed Hydrogels for Further Applications towards Water Treatment

In this work, novel chitosan-silica hydrogels were synthesized and investigated by various complementary techniques. The hydrogels were obtained via the immobilization of chitosan (Ch) on the surface of mesoporous cellular foams (MCFs). The latter silica materials were obtained by a sol-gel process, varying the composition of the reaction mixture (copolymer Pluronic 9400 or Pluronic 10500) and the ageing temperature conditions (80 °C or 100 °C). The role of the silica phase in the hydrogels was the formation of a scaffold for the biopolymeric chitosan component and providing chemical, mechanical, and thermal stability. In turn, the chitosan phase enabled the binding of anionic pollutions from aqueous solutions based on electrostatic interaction mechanisms and hydrogen bonds. To provide information on structural, morphological, and surface properties of the chitosan-silica hydrogels, analyses such as the low-temperature adsorption/desorption of nitrogen, small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier-transform infrared spectroscopy (FTIR) were performed. Moreover, the verification of the utility of the chitosan-silica hydrogels as adsorbents for water and wastewater treatment was carried out based on kinetic and equilibrium studies of the Acid Red 88 (AR88) adsorption. Adsorption data were analyzed by applying various equations and discussed in terms of the adsorption on heterogeneous solid-surfaces theory. The adsorption mechanism for the AR88 dye-chitosan-silica hydrogel systems was proposed.

Hierarchical Porous Aerogels With Multiple Adsorptive Interactions for Dye Wastewater Purification

Aerogels present a huge potential for removing organic dyes from printing and dyeing wastewater (PDW). However, the preparation of aerogels with multiple dye adsorption capabilities remains a challenge, as many existing aerogels are limited to adsorbing only a single type of dye. Herein, a composite aerogel (CG/T-rGO) with the addition of carboxymethyl chitosan, gelatin and tannic acid reduced graphene oxide (T-rGO) was synthesized by freeze-drying technology. The electrostatic interactions between dye molecular and GEL/CMCS (CG) networks, as well as the supramolecular interactions (H-bonds, electrostatic interactions and π-π stacks) between T-rGO, have endowed the aerogel with the ability to adsorb multiple types of dye, such as methylene blue (MB) and methyl orange (MO). Results exhibited that the prepared CG/T-rGO aerogel possessed strong mechanical strength and a porous 3D network structure with a porosity of 96.33 %. Using MB and MO as adsorbates, the adsorption capacity (88.2 mg/g and 66.6 mg/g, respectively) and the mechanism of the CG/T-rGO aerogel were investigated. The adsorption processes of aerogel for MB and MO were shown to follow the pseudo-second-order kinetic model and Langmuir isotherm model, indicating the chemical adsorption of a monolayer. The proposed aerogel in this work has promising prospects for dye removal from PDW.

Application of Activated Carbons Obtained from Polymer Waste for the Adsorption of Dyes from Aqueous Solutions

Plastic waste disposal is a major environmental problem worldwide. One recycling method for polymeric materials is their conversion into carbon materials. Therefore, a process of obtaining activated carbons through the carbonization of waste CDs (as the selected carbon precursor) in an oxygen-free atmosphere, and then the physical activation of the obtained material with CO2, was developed. Dyes such as methylene blue (MB) and malachite green (MG) are commonly applied in industry, which contaminate the water environment to a large extent and have a harmful effect on living organisms; therefore, adsorption studies were carried out for these cationic dyes. The effects of the activation time on the physicochemical properties of the activated materials and the adsorption capacity of the dyes were investigated. The obtained microporous adsorbents were characterized by studying the porous structure based on low-temperature nitrogen adsorption/desorption, scanning electron microscopy (SEM-EDS), elemental analysis (CHNS), Raman spectroscopy, X-ray powder diffraction (XRD), infrared spectroscopy (ATR FT-IR), thermal analysis (TG, DTG, DTA), Boehm's titration method, and pHpzc (the point of zero charge) determination. Moreover, adsorption studies (equilibrium and kinetics) were carried out. The maximum adsorption capacities (qm exp) of MB and MG (349 mg g-1 and 274 mg g-1, respectively) were identified for the obtained material after 8 h of activation. The results show that the use of waste CDs as a carbon precursor facilitates the production of low-cost and effective adsorbents.

Construction of Hierarchical Films via Layer-by-Layer Assembly of Exfoliated Unilamellar Zeolite Nanosheets

Zeolites have been widely applied as versatile catalysts, sorbents, and ion exchangers with unique porous structures showing molecular sieving capability. In these years, it is reported that some layered zeolites can be delaminated into molecularly thin 2-dimensional (2D) nanosheets characterized by inherent porous structures and highly exposed active sites. In the present study, two types of zeolite nanosheets with distinct porous structures with MWW topology (denoted mww) and ferrierite-related structure (denoted bifer) are deposited on a substrate through the solution process via electrostatic self-assembly. Alternate deposition of zeolite nanosheets with polycation under optimized conditions allows the layer-by-layer growth of their multilayer films with a stacking distance of 2-3 nm. Furthermore, various hierarchical structures defined at the unit-cell dimensions can be constructed simply by conducting the deposition of mww and bifer nanosheets in a designed sequence. Adsorption of a dye, Rhodamine B, in these films, is examined to show that adsorption is dependent on constituent zeolite nanosheets and their assembled nanostructures. This work has provided fundamental advancements in the fabrication of artificial zeolite-related hierarchical structures, which may be extended to other zeolite nanosheets, broadening their functionalities, applications, and benefits.

Graphene-Enhanced Methacrylated Alginate Gel Films for Sustainable Dye Removal in Water Purification

Self-standing nanocomposite films were prepared by three-dimensional UV-induced radical copolymerization of methacrylated alginate (MALG) with acrylic acid (AA) and reinforced with graphene oxide (GO) to improve both mechanical strength and dye adsorption capacity in wastewater decontamination operations. Dynamic mechanical-thermal analysis revealed variations in storage modulus: the higher the GO content, the higher the storage modulus (E') values. Also, the higher the temperature (associated with a lower and lower water content of films), the larger values of E' for the films of the same composition (E'(25 °C) = 676.6-1538.7 MPa; E'(100 °C) = 886.9-2066.6 MPa), providing insights into the compatibility between GO and the MALG/AA matrix, as well as, assessing the improvement in the nanocomposite's final mechanical properties. These crosslinked films in a dry state exhibited rapid water uptake and relatively short drying times (ca. 30 min at room temperature for the MALG/AA/GO composites) resulting from the swelling-drying studies and water contact angle measurements. The efficacy of methylene blue removal from water assessed via UV-VIS spectrometry revealed excellent results, expressed as an adsorption yield of 70-80% and 85-98% after 30 h and 258 h, respectively, of immersion time of films into an MB aqueous solution of 12.5 mg/L (as the contaminated water model). The reusability of the same films was evaluated by consecutive extraction processes of MB from the composite membranes when the content of desorbed dye was also spectrophotometrically monitored and conducted in acidic conditions (HCl aqueous solutions of pH 2). Overall, the introduction of GO in the developed self-standing MALG/AA nanocomposite films exhibited enhanced mechanical properties and increased efficiency for dye removal applications. Their great reutilization potential was highlighted by low drying times and a good ability to release the dye initially adsorbed. Thus, the prepared films could be suitable materials for sustainable and effective water treatment technologies.

Highly Sustainable Dyes Adsorption in Wastewater Using Textile Filters Fabricated by UV Irradiation

Vast amounts of dyeing wastewater released from the textile industry can not only cause water pollution but also have negative effects on the human body, such as skin irritation and respiratory diseases. Dye adsorption technology is necessary for the treatment of wastewater discharged from the dyeing industry and for environmental improvement. However, to remove dyeing wastewater, more energy and solvents are used to fabricate adsorbents, or excessive energy is used to filter dyeing wastewater out, resulting in more environmental pollution. Therefore, it is necessary to develop a method of filtering dyeing wastewater in a more environmentally friendly manner by minimizing the use of solvents and energy. In this study, we modified the surface of a textile substrate through UV irradiation to create a monomer capable of facilely bonding with dyes. Employing the UV photografting method, we were able to produce a dye adsorption filter in a more environmentally friendly manner, minimizing solvent usage and heat energy consumption required for absorbent synthesis. At a monomer concentration of 10%, the fabricated filter exhibited a dye removal efficiency of 97.34% after 24 h, all without the need for a pressure treatment or temperature increase. Moreover, it displayed an adsorption capacity of approximately 77.88 mg per 1 g of filter material.

Carbonized Leather Waste with Deposited Polypyrrole Nanotubes: Conductivity and Dye Adsorption

This paper reports the conversion of a waste to a conducting material, exploiting the ability to adsorb pollutant organic dyes. Leather waste was carbonized at 800 °C in an inert nitrogen atmosphere. The resulting biochar was used for in-situ deposition of polypyrrole nanotubes produced by the oxidative polymerization of pyrrole in the presence of methyl orange. The composites of carbonized leather with deposited polypyrrole nanotubes of various composition were compared with similar composites based on globular polypyrrole. Their molecular structure was characterized by infrared and Raman spectra. Both conducting components formed a bicontinuous structure. The resistivity was newly determined by a four-point van der Pauw method and monitored as a function of pressure applied up to 10 MPa. The typical conductivity of composites was of the order of 0.1 to 1 S cm-1 and it was always higher for polypyrrole nanotubes than for globular polypyrrole. The method also allows for the assessment of mechanical features, such as powder fluffiness. The conductivity decreased by 1-2 orders of magnitude after treatment with ammonia but still maintained a level acceptable for applications operating under non-acidic conditions. The composites were tested for dye adsorption, specifically cationic methylene blue and anionic methyl orange, using UV-vis spectroscopy. The composites were designed for future use as functional adsorbents controlled by the electrical potential or organic electrode materials.

Tailoring Homogeneous Hydrogel Nanospheres by Facile Ultra-Sonication Assisted Cross-Linked Copolymerization for Rhodamine B Dye Adsorption

The present paper describes the design of shape-oriented hydrogel nanospheres using a facile ultrasonication-supported crosslinked copolymerization technique. The effect of variable monomer concentration on the homogeneity of hydrogel nanospheres was investigated. The chitosan-cl-poly(MMA) hydrogel nanospheres were well characterized using various techniques such as FTIR, XRD, TGA, SEM, and TEM. The chitosan-cl-poly(MMA) hydrogel nanospheres were studied for their swelling behavior and could potentially be used as a novel adsorbent for rhodamine B dye remediation from aqueous media. The study found that utilizing chitosan-cl-poly(MMA) nanohydrogel spheres at the optimal pH 5 increased RhB dye adsorption capacity from 7.9 to 17.8 mg/g (pH 2 to 5), followed by a slight reduction. Furthermore, when nanohydrogel concentration increased, adsorption capacity dropped from 18.03 to 2.8 mg/g, but adsorption percentage climbed from 90.2% to 97.8%. At an initial dye concentration of 140 mg/L, rhodamine B adsorption achieved 204.3 mg/g in 60 min. The rhodamine B dye adsorption study includes adsorption kinetics, isotherm, and thermodynamics analyses. The interpretation of the adsorption study revealed that Langmuir isotherms fit best with a qmax value of 276.26 mg/g, which is in close approximation with the experimental value, whereas pseudo-second-order kinetics explains the adsorption process rate. The interaction of RhB dye with chitosan-cl-poly(MMA) hydrogel nanospheres involves multiple forces such as electrostatic interactions, hydrogen bonding, van der Waals forces, etc.

Reusable flexible poly(vinyl alcohol)/chitosan-based polymer carbon dots composite film for acid blue 93 dye adsorption

The design and synthesis of water-insoluble chitosan-based polymer carbon dots [P(CS-g-CA)CDs] are described. A polyvinyl alcohol/chitosan-based polymer carbon dot [PVA/P(CS-g-CA)CDs] composite film was prepared using a simple casting method to be used in dye adsorption. The composite film was characterized using FT-IR, XPS, transparency, contact angle, and mechanical properties tests, which showed the successful incorporation of P(CS-g-CA)CDs into the film and also revealed that hydrogen bonding improved the mechanical properties of the PVA film. Furthermore, the composite film displayed substantially enhanced hydrophobicity, making it suitable for use in aqueous environments. In addition, the composite film exhibited stable adsorption of acid blue 93 (AB93) at pH 2-9, with an enhanced adsorption capacity of 433.24 mg/g. The adsorption obeyed Langmuir law with an efficiency of more than 89% even after five cycles. Therefore, the PVA/P(CS-g-CA)CDs film is a promising material for the treatment of organic dye-polluted wastewater.

Effective Removal of Dyes from Wastewater by Osmanthus Fragrans Biomass Charcoal

The exploration of low-cost, high-performance adsorbents is a popular research issue. In this work, a straightforward method that combined hydrothermal with tube firing was used to produce Osmanthus fragrans biomass charcoal (OBC) from low-cost osmanthus for dye adsorption in water. The study examined the parameters of starting concentration, pH, and duration, which impacted the process of adsorption of different dyes by OBC. The analysis showed that the adsorption capacities of OBC for six dyes: malachite green (MG, C0 = 800 mg/L, pH = 7), Congo red (CR, C0 = 1000 mg/L, pH = 8), rhodamine B (RhB, C0 = 500 mg/L, pH = 6), methyl orange (MO, C0 = 1000 mg/L, pH = 7), methylene blue (MB, C0 = 700 mg/L, pH = 8), and crystalline violet (CV, C0 = 500 mg/L, pH = 7) were 6501.09, 2870.30, 554.93, 6277.72, 626.50, and 3539.34 mg/g, respectively. The pseudo-second-order model and the Langmuir isotherm model were compatible with the experimental findings, which suggested the dominance of ion exchange and chemisorption. The materials were characterized by using XRD, SEM, FTIR, BET, and XPS, and the results showed that OBC had an outstanding specific surface area (2063 m2·g-1), with potential adsorption mechanisms that included electrostatic mechanisms, hydrogen bonding, and π-π adsorption. The fact that the adsorption capacity did not drastically decrease after five cycles of adsorption and desorption suggests that OBC has the potential to be a dye adsorbent.

Development and Upscaling of SiO2@TiO2 Core-Shell Nanoparticles for Methylene Blue Removal

SiO2@TiO2 core-shell nanoparticles were successfully synthesized via a simple, reproducible, and low-cost method and tested for methylene blue adsorption and UV photodegradation, with a view to their application in wastewater treatment. The monodisperse SiO2 core was obtained by the classical Stöber method and then coated with a thin layer of TiO2, followed by calcination or hydrothermal treatments. The properties of SiO2@TiO2 core-shell NPs resulted from the synergy between the photocatalytic properties of TiO2 and the adsorptive properties of SiO2. The synthesized NPs were characterized using FT-IR spectroscopy, HR-TEM, FE-SEM, and EDS. Zeta potential, specific surface area, and porosity were also determined. The results show that the synthesized SiO2@TiO2 NPs that are hydrothermally treated have similar behaviors and properties regardless of the hydrothermal treatment type and synthesis scale and better performance compared to the SiO2@TiO2 calcined and TiO2 reference samples. The generation of reactive species was determined by EPR, and the photocatalytic activity was evaluated by the methylene blue (MB) removal in aqueous solution under UV light. Hydrothermally treated SiO2@TiO2 showed the highest adsorption capacity and photocatalytic removal of almost 100% of MB after 15 min in UV light, 55 and 89% higher compared to SiO2 and TiO2 reference samples, respectively, while the SiO2@TiO2 calcined sample showed 80%. It was also observed that the SiO2-containing samples showed a considerable adsorption capacity compared to the TiO2 reference sample, which improved the MB removal. These results demonstrate the efficient synergy effect between SiO2 and TiO2, which enhances both the adsorption and photocatalytic properties of the nanomaterial. A possible photocatalytic mechanism was also proposed. Also noteworthy is that the performance of the upscaled HT1 sample was similar to one of the lab-scale synthesized samples, demonstrating the potentiality of this synthesis methodology in producing candidate nanomaterials for the removal of contaminants from wastewater.

Chitosan-Silica Composites for Adsorption Application in the Treatment of Water and Wastewater from Anionic Dyes

A series of new types of composites (biopolymer-silica materials) are proposed as selective and effective adsorbents. A new procedure for the synthesis of chitosan-nanosilica composites (ChNS) and chitosan-silica gel composites (ChSG) using geometrical modification of silica and mechanosorption of chitosan is applied. The highest adsorption efficiency was achieved at pH = 2, hence the desirability of modifications aimed at stabilizing chitosan in such conditions. The amount of chitosan in the synthesis grew to 1.8 times the adsorption capacity for the nanosilica-supported materials and 1.6 times for the silica gel-based composites. The adsorption kinetics of anionic dyes (acid red AR88) was faster for ChNS than for ChSG, which results from a silica-type effect. The various structural, textural, and physicochemical aspects of the chitosan-silica adsorbents were analyzed via small-angle X-ray scattering, scanning electron microscopy, low-temperature gas (nitrogen) adsorption, and potentiometric titration, as well as their adsorption effectiveness towards selected dyes. This indicates the synergistic effect of the presence of dye-binding groups of the chitosan component, and the developed interfacial surface of the silica component in composites.

Application of a Mixed-Ligand Metal-Organic Framework in Photocatalytic CO2 Reduction, Antibacterial Activity and Dye Adsorption

In this paper, a known mixed-ligand MOF {[Co₂(TZMB)₂(1,4-bib)_0.5(H₂O)₂]·(H₂O)₂}_n (compound 1) was reproduced, and its potential application potential was explored. It was found that compound 1 had high photocatalytic activity for CO₂ reduction. After 12 h of illumination, the formation rate of CO, which is the product of CO₂ reduction by compound 1, reached 3012.5 μmol/g/h. At the same time, compound 1 has a good antibacterial effect on Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Candida albicans (C. albicans), which has potential research value in the medical field. In addition, compound 1 can effectively remove Congo Red from aqueous solutions and achieve the separation of Congo red from mixed dye solutions.

Complete Desorption of Hybrid Nanoclays Composed of Hydrotalcite and Disperse Dye

Clays are considered great nanoadsorbents for many materials, including textile dyes. The use of these materials for cleaning textile wastewater is well known; however, it is not at all common to find applications for the hybrid materials formed from the clay and dye. In this work, a dye-loaded clay material was used to make new dye baths and colour a polyester textile substrate. The same hybrid could be used several times as it did not use all the adsorbed dye in a single dyeing. The hybrid obtained from hydrotalcite (nanoclay) and the dispersed red 1 dye was analysed by measuring the colour obtained, carrying out an X-ray diffraction analysis that provided information after each desorption-dyeing process, and using infrared spectroscopy to analyse the specific bands of each characteristic group. Both analyses showed that the amount of dye present in the hybrid decreases. Thermogravimetry (TGA), surface area and porosity measurements (BET), and X-ray photoelectron spectroscopy (XPS) tests were conducted. Chemical stability was assessed by subjecting the hybrid to the actions of different reagents. In addition, colour fastness tests were carried out after dyeing and washing the polyester test tubes to check for the correct fixing of the dye to the fibre. These fastness results showed that the dyeing was carried out correctly and as if it was a conventional dyeing process.

Magnetic Nitrogen-Rich UiO-66 Metal-Organic Framework: An Efficient Adsorbent for Water Treatment

The postsynthetic modification of metal-organic frameworks (MOFs) has opened up a promising area to widen their water treatment application. However, their polycrystalline powdery state still restricts their widespread industrial-scale applications. Herein, the magnetization of UiO-66-NH₂ is reported as a promising approach to facilitate the separation of the used MOFs after water treatment. A two-step postmodification procedure employing 2,4,6-trichloro-1,3,5-triazine (TCT) and 5-phenyl-1H-tetrazole (PTZ) agents was introduced to level up the adsorption performance of the magnetic nanocomposite. Despite a decrement in porosity and specific surface area of the designed MOFs (m-UiO-66-TCT) compared to neat UiO-66-NH₂, it outweighs in adsorption capacity. It was observed that m-UiO-66-TCT has an adsorption capacity of ≈298 mg/g for methyl orange (MO) with facile MOF separation using an external magnet. Pseudo-second-order kinetic model and Freundlich isotherm models suitably interpret the experimental data. Thermodynamic studies showed that MO removal using m-UiO-66-TCT is spontaneous and thermodynamically favorable at higher temperatures. The m-UiO-66-TCT composite exhibited easy separation, high adsorption capacity, and good recyclability, rendering it an attractive candidate for the adsorptive removal of MO dye from aqueous environments.

Residual Chlorella-Based Cellulose Nanofibers and Their Quaternization Modification and Efficient Anionic Dye Adsorption

Dye is an anionic common pollutant in industrial wastewater and poses a great threat to the environment and human health. Owing to its advantageous adsorption capacity, nanocellulose is widely used for wastewater treatment. The cell walls of Chlorella mainly comprise cellulose instead of lignin. In this study, residual Chlorella-based cellulose nanofiber (CNF) and cationic cellulose nanofiber (CCNF) with surface quaternization were prepared through homogenization. Moreover, Congo red (CR) was used as a model dye to measure the adsorption capacity of CNF and CCNF. The adsorption capacity was almost saturated when CNF and CCNF contacted CR for 100 min, and the adsorption kinetics coincided with the pseudo-secondary kinetics model. The initial concentration of CR considerably affected its adsorption on CNF and CCNF. Below the initial concentration of 40 mg/g, the adsorption on CNF and CCNF considerably increased with the increase in the initial concentration of CR. Based on the sorption isotherms analysis of CNF and CCNF, the Langmuir model fitted best with the experimental data. Thus, CNF and CCNF surfaces were uniform, and monolayer adsorption occurred. The adsorption of CR on CNF and CCNF was greatly affected by the pH value, and the acidic medium favored the adsorption of CR (especially for CCNF). CCNF showed a more advantageous adsorption capacity, with a maximum value of 1657.89 mg/g, compared to that of CNF (190.0 mg/g). According to the findings of this study, residual Chlorella-based CCNF could be a very promising adsorbent candidate for removing anionic dyes from wastewater.

Magnetic Ionotropic Hydrogels Based on Carboxymethyl Cellulose for Aqueous Pollution Mitigation

In this work, stabilized ionotropic hydrogels were designed using sodium carboxymethyl cellulose (CMC) and assessed as inexpensive sorbents for hazardous chemicals (e.g., Methylene Blue, MB) from contaminated wastewaters. In order to increase the adsorption capacity of the hydrogelated matrix and facilitate its magnetic separation from aqueous solutions, sodium dodecyl sulfate (SDS) and manganese ferrite (MnFe₂O₄) were introduced into the polymer framework. The morphological, structural, elemental, and magnetic properties of the adsorbents (in the form of beads) were assessed using scanning electron microscopy (SEM), energy-dispersive X-ray analysis, Fourier-transform infrared spectroscopy (FTIR), and a vibrating-sample magnetometer (VSM). The magnetic beads with the best adsorption performance were subjected to kinetic and isotherm studies. The PFO model best describes the adsorption kinetics. A homogeneous monolayer adsorption system was predicted by the Langmuir isotherm model, registering a maximum adsorption capacity of 234 mg/g at 300 K. The calculated thermodynamic parameter values indicated that the investigated adsorption processes were both spontaneous (ΔG < 0) and exothermic (ΔH < 0). The used sorbent can be recovered after immersion in acetone (93% desorption efficiency) and re-used for MB adsorption. In addition, the molecular docking simulations disclosed aspects of the mechanism of intermolecular interaction between CMC and MB by detailing the contributions of the van der Waals (physical) and Coulomb (electrostatic) forces.

Triazine-Based Porous Organic Polymers: Synthesis and Application in Dye Adsorption and Catalysis

The scientific community has been developing promising materials to increase the sustainability and efficiency of production processes and pollutant environmental remediation strategies. Porous organic polymers (POPs) are of special interest, as they are insoluble custom-built materials at the molecular level, endowed with low densities and high stability, surface areas, and porosity. This paper describes the synthesis, characterization, and performance of three triazine-based POPs (T-POPs) in dye adsorption and Henry reaction catalysis. T-POPs were prepared by a polycondensation reaction between melamine and a dialdehyde (terephthalaldehyde (T-POP1) or isophthalaldehyde derivatives with a hydroxyl group (T-POP2) or both a hydroxyl and a carboxyl group (T-POP3)). The crosslinked and mesoporous polyaminal structures, with surface areas between 139.2 and 287.4 m² g^-1, positive charge, and high thermal stability, proved to be excellent methyl orange adsorbents, removing the anionic dye with an efficiency >99% in just 15-20 min. The POPs were also effective for methylene blue cationic dye removal from water, reaching efficiencies up to ca. 99.4%, possibly due to favorable interactions via deprotonation of T-POP3 carboxyl groups. The modification of the most basic polymers, T-POP1 and T-POP2, with copper(II) allowed the best efficiencies in Henry reactions catalysis, leading to excellent conversions (97%) and selectivities (99.9%).

Dyeing with Hydrotalcite Hybrid Nanoclays and Disperse, Basic and Direct Dyes

Textile effluents are among the most polluting industrial effluents in the world. Textile finishing processes, especially dyeing, discharge large quantities of waste that is difficult to treat, such as dyes. By recovering this material from the water, in addition to cleaning and the possibility of reusing the water, there is the opportunity to reuse this waste as a raw material for dyeing different textile substrates. One of the lines of reuse is the use of hybrid nanoclays obtained from the adsorption of dyes, which allow dye baths to be made for textile substrates. This study analyses how, through the use of the nanoadsorbent hydrotalcite, dyes classified by their charge as anionic, cationic and non-ionic can be adsorbed and recovered for successful reuse in new dye baths. The obtained hybrids were characterised by X-ray diffraction and infrared spectroscopy. In addition, the colour was analysed by spectrophotometer in the UV-VIS range. The dyes made on cotton, polyester and acrylic fabrics are subjected to different colour degradation tests to assess their viability as final products, using reflection spectroscopy to measure the colour attribute before and after the tests, showing results consistent with those of a conventional dye.

Triangular Heteroporous Covalent Organic Framework via a K-Shaped "Two-in-One" Monomer: Targeted Synthesis and Selective Removal of Organic Pollutants

Covalent organic frameworks (COFs) have attracted increasing research interest due to their intriguing topological structures and fascinating properties. Diverse COFs with different shapes and sizes are developed by the design of appropriate building blocks. However, the heteroporous COFs to date are still in their infancy due to the relatively limited configuration of precursors. Herein, it is ingeniously designed and synthesized a new K-shaped "two-in-one" building unit (3',6'-bis(4-(5,5-dimethyl-1,3-dixoan-2-yl)phenyl)-[1,1':2',1"-terphenyl]-4,4"-diamine, BPTD), thus realizing the construction of triangular dual microporous COF (BPTD-COF) via self-polycondensation of the K-shaped monomer. The super micropore (0.76 nm) of BPTD-COF endows the higher density of amine activity sites, while the other aperture size (1.35 nm) meets the need for accommodating cationic dyes (rhodamine B, methylene blue), thus BPTD-COF displays a distinctive selective adsorption for cationic dyes with good reusability.

Performance of Dye Removal from Single and Binary Component Systems by Adsorption on Composite Hydrogel Beads Derived from Fruits Wastes Entrapped in Natural Polymeric Matrix

The treatment of contaminated water is currently a major concern worldwide. This work was directed towards the preparation of a composite hydrogel by entrapping cherry stones powder on chitosan, which is known as one of the most abundant natural polymers. The synthesized material was characterized by scanning electron microscopy, by Fourier transform infrared spectroscopy, and by the point of zero charge determination. Its ability to remove two azo dyes models (Acid Red 66 and Reactive Black 5) existing in single form and in binary mixture was evaluated. Response Surface Methodology-Central Composite Design was used to optimize three parameters affecting the process while targeting the lowest final contaminant concentrations. The best results were obtained at pH 2, an adsorbent dose of 100 g/L, and a temperature of 30 °C, when more than 90% of the pollutants from the single component systems and more than 70% of those of the binary mixtures were removed from their aqueous solutions. The adsorption process was in accordance with Elovich and pseudo-second-order kinetic models, and closely followed the Freundlich and Temkin equilibrium isotherms. The obtained results led to the conclusion that the prepared hydrogel composite possesses the ability to successfully retain the target molecules and that it can be considered as a viable adsorbent material.

Layered Double Hydroxide-Bismuth Molybdate Hybrids toward Water Remediation via Selective Adsorption of Anionic Species

The steady release of anthropogenic toxins into the biosphere is compromising water security globally. Herein, CoAl layered double hydroxide, a clay-like layered material with a cationic surface charge, was organically modified and used to template the growth of Bi₂MoO₆. The resulting nanohybrid selectively removed the anionic dye methyl orange from aqueous solution and showed an enhancement of greater than 300% in the maximum adsorptivity (1.95 mmol/g) compared to modified CoAl layered double hydroxide (0.42 mmol/g). Interestingly, the observed improvement in adsorption occurs without any significant increase in the surface area of the hybrids. Furthermore, these hybrids exhibit increased broadband visible light absorption, and their photoactivity is slightly improved compared to CoAl layered double hydroxide. This study demonstrates that composites of clay-like materials with Aurivillius oxides are promising sorbent materials for water decontamination and photocatalytic antifouling membranes and shows that the synthetic strategy that was first established with an anionic layered silicate nanoclay can be generalized to other ionic layered materials.

Self-Assembly of a Graphene Oxide Liquid Crystal for Water Treatment

Adsorbents, especially those with high removal efficiency, long life, and multi-purpose capabilities, are the most crucial components in an adsorption system. By taking advantage of the liquid-like mobility and crystal-like ordering of liquid crystal materials, a liquid crystal induction method is developed and applied to construct three-dimensional graphene-based adsorbents featuring excellent shape adaptability, a distinctive pore structure, and abundant surface functional groups. When the monoliths are used for water restoration, the large amount of residual oxygen-containing groups is more susceptible to electrophilic attack, thus contributing to cation adsorption (up to 705.4 mg g^-1 for methylene blue), while the connected microvoids between the aligned graphene oxide sheets facilitate mass transfer, e.g., the high adsorption capacity for organic pollutants (196.2 g g^-1 for ethylene glycol) and the high evaporation rate for water (4.01 kg m^-2 h^-1). This work gives a practical method for producing high-performance graphene-based functional materials for those applications that are sensitive to surface and mass transfer properties.

Tetrazolyl Porphyrin-Based Hydrogen-Bonded Organic Frameworks: Active Sites-Mediated Host-Guest Synergy for Advanced Antimicrobial Applications

Hydrogen-bonded organic frameworks (HOFs) with multiple functions and permanent pores have received widespread attention due to their potential applications in gas adsorption/separation, drug delivery, photocatalysis, proton conduction, and other fields. Herein, we constructed a three-dimensional (3D) HOF with 1D square channels by utilizing a dual-functional tetrazolyl porphyrin ligand bearing an active center of the porphyrin core and open sites of nitrogen atoms through π-π stacking and hydrogen-bonding interaction self-assembly. The structure exhibits both solvent resistance and thermal stability, and especially, maintains these after being transformed into nanoparticles. Meanwhile, the active sites exposed on the inner wall of the pores can interact well with the photoactive cationic dye molecules to form an effective host-guest (H-G) system, which can realize boosted photosensitized singlet oxygen (1O2) production under red light irradiation and synergistic sterilization toward Staphylococcus aureus (S. aureus) with an inhibition ratio as high as 99.9%. This work provides a valuable design concept for HOF-related systems in pursuit of promoted photoactivity.

A Peptide-Based Hydrogel for Adsorption of Dyes and Pharmaceuticals in Water Remediation

The removal of dyes and pharmaceuticals from water has become a major issue in recent years due to the shortage of freshwater resources. The adsorption of these pollutants through nontoxic, easy-to-make, and environmentally friendly adsorbents has become a popular topic. In this work, a tetrapeptide-pyrene conjugate was rationally designed to form hydrogels under controlled acidic conditions. The hydrogels were thoroughly characterized, and their performance in the adsorption of various dyes and pharmaceuticals from water was investigated. The supramolecular hydrogel efficiently adsorbed methylene blue (MB) and diclofenac (DCF) from water. The effect of concentration in the adsorption efficiency was studied, and results indicated that while the adsorption of MB is governed by the availability of adsorption sites, in the case of DCF, concentration is the driving force of the process. In the case of MB, the nature of the dye-hydrogel interactions and the mechanism of the adsorption process were investigated through UV-Vis absorption spectroscopy. The studies proved how this dye is first adsorbed as a monomer, probably through electrostatic interactions; successively, at increasing concentrations as the electrostatic adsorption sites are depleted, dimerization on the hydrogel surface occurs.

Recent Advances in the Removal of Organic Dyes from Aqueous Media with Conducting Polymers, Polyaniline and Polypyrrole, and Their Composites

Water pollution by organic dyes, and its remediation, is an important environmental issue associated with ever-increasing scientific interest. Conducting polymers have recently come to the forefront as advanced agents for removing dye. The present review reports on the progress represented by the literature published in 2020–2022 on the application of conducting polymers and their composites in the removal of dyes from aqueous media. Two composites, incorporating the most important polymers, polyaniline, and polypyrrole, have been used as efficient dye adsorbents or photocatalysts of dye decomposition. The recent application trends are outlined, and future uses also exploiting the electrical and electrochemical properties of conducting polymers are offered.

Template Method for Synthesizing Hierarchically Porous MIL-101(Cr) for Efficient Removal of Large Molecular Dye

As one of the most important prototypical chromium-based MOFs, MIL-101(Cr) is well-studied and widely employed in various scientific fields. However, due to its small capture window sizes and curved internal apertures, its application in large molecular removal is quite limited, and given its high stability and high synthetic temperature (>200 °C), it is difficult to achieve hierarchically porous MIL-101(Cr). In our study, hierarchically porous MIL-101(Cr) involving a high macro-/meso-/micropores ratio was designed and synthesized using acetic acid as an additive and silicon dioxide (SiO2) nanoparticles as a template. The optimal hierarchically porous MIL-101(Cr) (A-4) possessed a high specific surface area (2693 m2 g−1) and an abundant macro-/mesoporous structure with the addition of SiO2 of 200 mg. Compared with the control sample (A-0) with a less macro-/mesoporous structure, A-4 showed good adsorption properties for both coomassie brilliant blue R-250 (CBB, 82.1 mg g−1) and methylene blue (MB, 34.3 mg g−1) dyes, which were 1.36 times and 9.37 times higher than those of A-0. Moreover, A-4 also had good recyclability, and the removal rate of CBB was still higher than 85% after five cycles of adsorption.

Cellulose Nanofibrils as a Damping Material for the Production of Highly Crystalline Nanosized Zeolite Y via Ball Milling

Nanosized zeolite Y is used in various applications from catalysis in petroleum refining to nanofillers in water treatment membranes. Ball milling is a potential and fast technique to decrease the particle size of zeolite Y to the nano range. However, this technique is associated with a significant loss of crystallinity. Therefore, in this study, we investigate the effect of adding biodegradable and recyclable cellulose nanofibrils (CNFs) to zeolite Y in a wet ball milling approach. CNFs are added to shield the zeolite Y particles from harsh milling conditions due to their high surface area, mechanical strength, and water gel-like format. Different zeolite Y to CNFs ratios were studied and compared to optimize the ball milling process. The results showed that the optimal zeolite Y to CNFs ratio is 1:1 to produce a median particle size diameter of 100 nm and crystallinity index of 32%. The size reduction process provided accessibility to the zeolite pores and as a result increased their adsorption capacity. The adsorption capacity of ball-milled particles for methylene blue increased to 29.26 mg/g compared to 10.66 mg/g of the pristine Zeolite. These results demonstrate the potential of using CNF in protecting zeolite Y particles and possibly other micro particles during ball milling.

Pyrene-based sulfonated organic porous materials for rapid adsorption of cationic dyes in water

Porous organic polymers (POP) have gained attention because of their high specific surface area, porosity and their simplicity in synthesis, but for the most part, they are hydrophobic because of their organic backbone, making it difficult to expand their applications. Here, we have obtained poly(pyrene) porous organic polymers (PyPOP) through the polymerization of pyrene monomers catalysed by aluminium trichloride, which is a simple and inexpensive synthesis method. The sulfonated poly(pyrene) porous organic polymers (PyPOP-SO₃H) obtained showed rapid adsorption of cationic dyes, especially malachite green (MG adsorption 1607 mg/g) and methylene blue (MB adsorption 1220 mg/g) in pH = 7 aqueous solution, room temperature. The results show that the Freundlich model is more in line with the adsorption process than the Langmuir model, whether for methylene blue or malachite green. In addition, the PSO kinetic model fits better than PFO kinetic model, whether it is for the adsorption of methylene blue or malachite green. The excellent adsorption performance of PyPOP-SO3H for cationic dyes may be due to the introduction of sulfonic acid groups, which not only increases the specific surface area but also allows better dispersion in water, increasing contact points and adsorption efficiency. This research expands the scope of exploration and application of POP.

Surface-Encapsulated Bismuth Molybdate-Layered Silicate Hybrids as Sorbents for Photocatalytic Filtration Membranes

Groundwater is being depleted globally at an average rate of more than one meter per year, during a period when more than a quarter of the human population has no access to potable water. Aside from overexploitation, freshwater security is also threatened by climate change and chemical pollution. The contamination of surface and groundwater by industrial substances is also undermining the vitality of ecosystems. It was previously shown that {100}-faceted Bi2MoO6-Laponite hybrids effectively bind and photodegrade molecular species, aiding in the decontamination of water. In this study, the encapsulation of Bi2MoO6-Laponite particles with the polymers butyl acrylate and styrene further enhanced adsorption of methylene blue by 31.4%, with a specific adsorption capacity of 192 μmol/g. The polymer-particle composites were deposited to form membranes and their efficacies in water filtration and photodegradation were examined. Among the different surface modifications examined, the highest dye sorption was obtained by butyl acrylate and styrene (3:2) with a 5 mol % cross-linker. This study provides a method for enhancing the molecular adsorption of composite particles used in membranes capable of multiple cycles of adsorption and photodegradation, advancing the application of such systems to water filtration.

Solution Blow Spun Silica Nanofibers: Influence of Polymeric Additives on the Physical Properties and Dye Adsorption Capacity

The physical properties of porous silica nanofibers are an important factor that impacts their performance in various applications. In this study, porous silica nanofibers were produced via solution blow spinning (SBS) from a silica precursor/polymer solution. Two polyvinylpyrrolidone (PVP, M_w = 360,000 and 1,300,000) were chosen as spinning aids in order to create different pore properties. The effect of their physical properties on the adsorption of methylene blue (MB) in an aqueous solution was explored. After forming, the nanofibers were calcined to remove the organic phase and create pores. The calcined nanofibers had a large amount of micro and mesopores without the use of additional surfactants. The molecular weight of the PVP impacted the growth of silica particles and consequently the pore size. High M_w PVP inhibited the growth of silica particles, resulting in a large volume of micropores. On the other hand, silica nanofibers with a high fraction of mesopores were obtained using the lower M_w PVP. These results demonstrate a simple method of producing blow spun silica nanofibers with defined variations of pore sizes by varying only the molecular weight of the PVP. In the adsorption process, the accessible mesopores improved the adsorption performance of large MB molecules.

Kinetic and mechanistic study of dye sorption onto renewable resource-based doped carbon prepared by a microwave-assisted method

Herein, a facile synthesis of heteroatom doped biochar is reported. The material is characterized and analyzed in detail for its application as a low-cost adsorbent for removal of a toxic dye pollutant, Methylene Blue (MB), from aqueous solution. Synthesized material showed enhanced surface area compared to parent biochar (458 to802 m²g^-1) The adsorbent's performance is investigated using batch adsorption methods with experiments conducted at varying conditions of adsorbent dosage, initial dye concentration (50-500 mg/L), and pH (3-11). Adsorption of MB onto two different adsorbents such as biochar (BC) and doped BC, is fitted using Langmuir and Freundlich isotherms with the experimental data correlating most accurately with Langmuir modelling, indicating chemisorption mechanism of dye onto adsorbent. Maximum monolayer equilibrium adsorption from Langmuir equation is found to be 129.8 and 357.1 mg/g for pure BC and Phosphorus and Nitrogen co-doped BC (PNBC), respectively. Pseudo-first and -second order kinetic models are applied to investigate the adsorption mechanism of PNBC. Adsorption mechanism followed pseudo-second order model well, with correlation coefficients very close to 1. The results indicate that microwave-assisted heteroatom co-doped BC showed superior performance as adsorbent for the adsorption of MB dye from aqueous solution.

Statistically Optimum HKUST-1 Synthesized by Room Temperature Coordination Modulation Method for the Adsorption of Crystal Violet Dye

Due to its excellency and versatility, many synthesis methods and conditions were developed to produce HKUST-1 ([Cu3(BTC)2(H2O)3]n). However, the diversity of HKUST-1 was actually generated both in terms of characteristics and morphologies. Hence, the consistency of HKUST-1 characteristics and morphologies needs to be maintained. The statistical analysis and optimization provide features to determine the best synthesis condition. Here, a room-temperature coordination modulation method was proposed to maintain the morphology of HKUST-1 while reducing energy consumption. In addition, response surface methodology (RSM) was used to demonstrate the statistical analysis and optimization of the synthesis of HKUST-1. The molar ratio of ligand to metal, reaction time, and acetic acid concentration were studied to determine their effects on HKUST-1. The optimum HKUST-1 was obtained by the synthesis with a molar ratio of ligand to metal of 0.4703 for 27.2 h using 5% v/v acetic acid concentration. The statistical analysis performed a good agreement with the experimental data and showed the significance of three desired parameters on HKUST-1. The optimum HKUST-1 had the adsorption capacity of 1005.22 mg/g with a removal efficiency of 92.31% towards CV dye. It could be reused up to 5 cycles with insignificant decrease in performance.

A Study on Machine Learning Methods' Application for Dye Adsorption Prediction onto Agricultural Waste Activated Carbon

The adsorption of dyes using 39 adsorbents (16 kinds of agro-wastes) were modeled using random forest (RF), decision tree (DT), and gradient boosting (GB) models based on 350 sets of adsorption experimental data. In addition, the correlation between variables and their importance was applied. After comprehensive feature selection analysis, five important variables were selected from nine variables. The RF with the highest accuracy (R² = 0.9) was selected as the best model for prediction of adsorption capacity of agro-waste using the five selected variables. The results suggested that agro-waste characteristics (pore volume, surface area, agro-waste pH, and particle size) accounted for 50.7% contribution for adsorption efficiency. The pore volume and surface area are the most important influencing variables among the agro-waste characteristics, while the role of particle size was inconspicuous. The accurate ability of the developed models’ prediction could significantly reduce experimental screening efforts, such as predicting the dye removal efficiency of agro-waste activated carbon according to agro-waste characteristics. The relative importance of variables could provide a right direction for better treatments of dyes in the real wastewater.

Preparation of core-shell structured polystyrene @ graphene oxide composite microspheres with high adsorption capacity and its removal of dye contaminants

Styrene was added dropwise to graphene dispersion solution by Pickering emulsion method to fabricate polystyrene @ graphene oxide layered composite microspheres (Pst@GO) for the removal of dye pollutants from water solution. Field emission scanning electron microscope, transmission electron microscopy, energy dispersive spectrometer, Brunauer emmett teller, zeta potential analyser and Fourier transform infrared spectrometer were adopted to analyse the changes in the microstructure and functional group of Pst@GO before and after the adsorption. The effects of initial concentration, adsorbent dose, pH, adsorption temperature and time on the adsorption behaviour of RhB and MB onto Pst@GO were studied by batch experiments. The results showed that a lot of folds on the surface of Pst@GO were beneficial to improve its adsorption capacity. The maximum adsorption capacity of RhB and MB onto Pst@GO was 49.70 and 59.07 mg g^-1 at the initial concentration of 300 mg L^-1, dose 0.1 g, pH = 7.0, adsorption temperature 55°C, adsorption time 2 h. The adsorption kinetics and thermodynamics analysis indicated that the adsorption of two dyes onto Pst@GO was endothermic reaction, while electrostatic attraction and hydrogen bonding are the main driving forces for the adsorption reaction.Polystyrene @ graphene oxide layered composite microspheres (Pst@GO) were prepared by Pickering emulsion method to remove dye pollutants in water. The preparation process of Pst@GO is as follows:Figure 1 Schematic fabrication process of Pst@GO.

Facile Microwave Hydrothermal Synthesis of ZnFe2O4/rGO Nanocomposites and Their Ultra-Fast Adsorption of Methylene Blue Dye

The industry development in the last 200 years has led to to environmental pollution. Dyes emitted by pharmaceutical and other industries are major organic pollutants. Organic dyes are a pollutant that must be removed from the environment. In this work, we adopt a facile microwave hydrothermal method to synthesize ZnFe2O4/rGO (ZFG) adsorbents and investigate the effect of synthesis temperature. The crystal structure, morphology, chemical state, and magnetic property of the nanocomposite are investigated by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and a vibrating sample magnetometer. Furthermore, the synthesized ZFGs are used to remove methylene blue (MB) dye, and the adsorption kinetics, isotherm, mechanism, and reusability of this nanomaterial are studied. The optimal ZFG nanocomposite had a dye removal percentage of almost 100%. The fitting model of adsorption kinetics followed the pseudo-second-order model. The isotherm model followed the Langmuir isotherm and the theoretical maximum adsorption capacity of optimal ZFG calculated by this model was 212.77 mg/g. The π-π stacking and electrostatic interaction resulted in a high adsorption efficiency of ZFG for MB adsorption. In addition, this nanocomposite could be separated by a magnet and maintain its dye removal percentage at almost 100% removal after eight cycles, which indicates its high suitability for utilization in water treatment.

Core-Shell Structured Magnetic Carboxymethyl Cellulose-Based Hydrogel Nanosorbents for Effective Adsorption of Methylene Blue from Aqueous Solution

This article reports effective removal of methylene blue (MB) dyes from aqueous solutions using a novel magnetic polymer nanocomposite. The core-shell structured nanosorbents was fabricated via coating Fe₃O₄ nanoparticles with a layer of hydrogel material, that synthesized by carboxymethyl cellulose cross-linked with poly(acrylic acid-co-acrylamide). Some physico-chemical properties of the nanosorbents were characterized by various testing methods. The nanosorbent could be easily separated from aqueous solutions by an external magnetic field and the mass fraction of outer hydrogel shell was 20.3 wt%. The adsorption performance was investigated as the effects of solution pH, adsorbent content, initial dye concentration, and contact time. The maximum adsorption capacity was obtained at neutral pH of 7 with a sorbent dose of 1.5 g L⁻¹. The experimental data of MB adsorption were fit to Langmuir isotherm model and Pseudo-second-order kinetic model with maximum adsorption of 34.3 mg g⁻¹. XPS technique was applied to study the mechanism of adsorption, electrostatic attraction and physically adsorption may control the adsorption behavior of the composite nanosorbents. In addition, a good reusability of 83.5% MB recovering with adsorption capacity decreasing by 16.5% over five cycles of sorption/desorption was observed.

Proteases Production and Chitin Preparation from the Liquid Fermentation of Chitinous Fishery By-Products by Paenibacillus elgii

Chitinous fishery by-products have great application in the production of various bioactive compounds. In this study, Paenibacillus elgii TKU051, a protease-producing bacterial strain, was isolated using a medium containing 1% squid pens powder (SPP) as the sole carbon/nitrogen (C/N) source. P. elgii TKU051 was found to produce at least four proteases with molecular weights of 100 kDa, 57 kDa, 43 kDa, and 34 kDa (determined by the gelatin zymography method). A P. elgii TkU051 crude enzyme cocktail was optimally active at pH 6-7 and 60 °C. The 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity and α-glucosidase inhibitory activity of the hydrolysates obtained from the hydrolysis of shrimp shell powder, shrimp head powder, shrimp meat powder, fish head powder and soya bean powder catalyzed by the P. elgii TkU051 crude enzyme cocktail were also evaluated. P. elgii TKU051 exhibited a high deproteinization capacity (over 94%) on different kinds of shrimp waste (shrimp heads and shells; fresh and cooked shrimp waste; shrimp waste dried by oven and lyophilizer), and the Fourier-transform infrared spectroscopy profile of the chitin obtained from the deproteinization process displayed the characteristic of chitin. Finally, the obtained chitin exhibited an effect comparable to commercial chitin in terms of adsorption against Congo Red (90.48% and 90.91%, respectively). Thus, P. elgii TKU051 showed potential in the reclamation of chitinous fishery by-products for proteases production and chitin extraction.

Optimizing Fe-Based Metal-Organic Frameworks through Ligand Conformation Regulation for Efficient Dye Adsorption and C2 H2 /CO2 Separation

Regulating the structure of metal-organic frameworks (MOFs) by adjusting the ligands reasonably is expected to enhance the interaction of MOFs on special molecules/ions, which has significant application value for the selective adsorption of guest molecules. Herein, two tricarboxylic ligands H₃ L-Cl and H₃ L-NH₂ were designed and synthesized based on the ligand H₃ TTCA by replacing part of the benzene rings with C=C bonds and modifying the chlorine and amino groups on the 4-position of the benzene ring. Two 3D Fe-MOFs (UPC-60-Cl and UPC-60-NH₂ ) with the new topology types were constructed. As the C=C bonds of the ligands have flexible torsion angles, UPC-60-Cl features three types of irregular 2D channels, while UPC-60-NH₂ has a cage with two types of windows on the surface. The synergistic effect of unique channels and modification of functional groups endows UPC-60-Cl and UPC-60-NH₂ with high adsorption capacity for organic dyes. Compound UPC-60-Cl shows high adsorption capacity for CV (147.2 mg g^-1 ), RHB (100.3 mg g^-1 ), and MO (220.9 mg g^-1 ), whereas UPC-60-NH₂ exhibits selective adsorption of MO (158.7 mg g^-1 ). Meanwhile, based on the diverse pore structure and modification of active sites, UPC-60-Cl and UPC-60-NH₂ show the selective separation of equimolar C₂ H₂ /CO₂ . Therefore, reasonable regulation of organic ligands plays a significant role in guiding the structure diversification and performance improvement of MOFs.

Carbon Adsorbents from Spent Coffee for Removal of Methylene Blue and Methyl Orange from Water

Activated carbons (ACs) were prepared from dried spent coffee (SCD), a biological waste product, to produce adsorbents for methylene blue (MB) and methyl orange (MO) from aqueous solution. Pre-pyrolysis activation of SCD was achieved via treatment of the SCD with aqueous sodium hydroxide solutions at 90 °C. Pyrolysis of the pretreated SCD at 500 °C for 1 h produced powders with typical characteristics of AC suitable and effective for dye adsorption. As an alternative to the rather harsh base treatment, calcium carbonate powder, a very common and abundant resource, was also studied as an activator. Mixtures of SCD and CaCO₃ (1:1 w/w) yielded effective ACs for MO and MB removal upon pyrolysis needing only small amounts of AC to clear the solutions. A selectivity of the adsorption process toward anionic (MO) or cationic (MB) dyes was not observed.

Silsesquioxane-Based Triphenylamine-Linked Fluorescent Porous Polymer for Dyes Adsorption and Nitro-Aromatics Detection

In order to enrich hybrid materials, a novel fluorescent silsesquioxane-based polymer (denoted as PCS-OTS) was synthesized by Friedel-Crafts reaction starting from octavinylsilsesquioxane (OVS) with triphenylamine-functionalized silsesquioxane monomer (denoted as OTS) with AlCl₃ as catalyst. PCS-OTS possessed a high surface area of 816 m²/g and a unique bimodal pore structure. The triphenylamine unit endowed PCS-OTS with excellent luminescence, which made it act as a sensitive chemical sensor and detect p-nitrophenol with high sensitivity (K_SV = 81,230 M^-1). Moreover, PCS-OTS can significantly remove dyes, and the respective adsorption capacity for Rhodamine B (RB), Congo red (CR) and Methyl Orange (MO) is 1935, 1420 and 155 mg/g. Additionally, it could simultaneously remove multiple dyes from water by simple filtration and be easily regenerated. This hybrid porous polymer can be a good choice for water treatment.

Cyclodextrin-Cross-Linked Hydrogels for Adsorption and Photodegradation of Cationic Dyes in Aqueous Solution

Possessing three-dimensional porous structures and tunable mechanical strengths, cyclodextrin-containing polymeric hydrogels are one of the most promising water-based adsorbent materials due to their easy availability, simple chemical modification and environmental friendliness. In this work, two kinds of hydrogels were prepared via the copolymerization with acrylic acid and vinyl-derivatized β-cyclodextrins in water. These two gels have showed good adsorption performance towards cationic dyes through the noncovalent interactions with their anionic backbones and porous network. Meanwhile, pseudo-second-order model was selected to clarify the adsorption kinetics process. Moreover, nano-scaled TiO₂ was doped into these resultant cyclodextrins-based hydrogels to achieve efficient degradation of dyes upon light irradiation. The obtained TiO₂ -loaded hydrogels could exhibit improved adsorption performance and make the adsorbed dyes photo-degraded with the decolorization rates above 95%. It can be envisioned that such cyclodextrin-based soft materials may find applications in dye clearance and water treatment.

Metal Cation Triggered Peptide Hydrogels and Their Application in Food Freshness Monitoring and Dye Adsorption

Metal-ligand interactions have emerged as an important tool to trigger and modulate self-assembly, and to tune the properties of the final supramolecular materials. Herein, we report the metal-cation induced self-assembly of a pyrene-peptide conjugate to form hydrogels. The peptide has been rationally designed to favor the formation of β-sheet 1D assemblies and metal coordination through the Glu side chains. We studied in detail the self-assembly process in the presence of H+, Li+, Na+, K+, Ca2+, Ni2+, Cu2+, Zn2+, Cd2+, Co2+, Fe3+, and Cr3+ and found that the morphology and mechanical properties of the hydrogels are ion-dependent. Moreover, thanks to the presence of the metal, new applications could be explored. Cu2+ metallogels could be used for amine sensing and meat freshness monitoring, while Zn2+ metallogels showed good selectivity for cationic dye adsorption and separation.

Carbon dots crosslinked chitosan/cellulose sponge capture of methyl blue by an adsorption process

For environmental protection, organic dyes and solvents of industrial wastewater must be eliminated. Here, a citric acid-based carbon dots (CA-CDs) crosslinked chitosan/microcrystalline cellulose (CS/MCC/CA-CDs) sponge was synthesized to study its adsorption performance for methyl blue (MB) dye. The morphology of the sponge was a tangled fibre with a bundle formed by hydrogen bonds between CA-CDs and the CS/MCC composite matrix. The abundant amount of tangled fibre bundle units can offer plentiful active adsorption sites to collect the dye molecules. The adsorption capacity of the CS/MCC/CA-CDs sponge toward MB was 306.8 mg/g at pH 10 and a temperature of 298 K. In addition, the pseudo-second-order kinetic model was matched with the adsorption kinetic experimental data, and the adsorption isotherm data can be described by the Langmuir models. This study proposed that the CS/MCC/CA-CDs sponge adsorbent creates tremendous potential application value in wastewater treatment due to its fast kinetics, high adsorption capacity, simple preparation, and eco-friendly properties.

Methylene Blue Dye Adsorption from Wastewater Using Hydroxyapatite/Gold Nanocomposite: Kinetic and Thermodynamics Studies

The present work demonstrates the development of hydroxyapatite (HA)/gold (Au) nanocomposites to increase the adsorption of methylene blue (MB) dye from the wastewater. HA nanopowder was prepared via a wet chemical precipitation method by means of Ca(OH)₂ and H₃PO₄ as starting materials. The biosynthesis of gold nanoparticles (AuNPs) has been reported for the first time by using the plant extract of Acrocarpus fraxinifolius. Finally, the as-prepared HA nanopowder was mixed with an optimized AuNPs solution to produce HA/Au nanocomposite. The prepared HA/Au nanocomposite was studied by using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Analysis (EDX) analysis. Adsorption studies were executed by batch experiments on the synthesized composite. The effect of the amount of adsorbent, pH, dye concentration and temperature was studied. Pseudo-first-order and pseudo-second-order models were used to fit the kinetic data and the kinetic modeling results reflected that the experimental data is perfectly matched with the pseudo-first-order kinetic model. The dye adsorbed waste materials have also been investigated against Pseudomonas aeruginosa, Micrococcus luteus, and Staphylococcus aureus bacteria by the agar well diffusion method. The inhibition zones of dye adsorbed samples are more or less the same as compared to as-prepared samples. The results so obtained indicates the suitability of the synthesized sample to be exploited as an adsorbent for effective treatment of MB dye from wastewater and dye adsorbed waste as an effective antibacterial agent from an economic point of view.

Super and Selective Adsorption of Cationic Dyes onto Carboxylate-Modified Passion Fruit Peel Biosorbent

The carboxylate-functionalized passion fruit peel (PFPCS) was an efficient and rapid biosorbent for wastewater treatment. The PFPCS exhibited excellent selectivity to the cationic dyes, where the maximum adsorption capacities for methylene blue (MB) and methyl violet (MV) were 1,775.76 mg g-1 and 3,756.33 mg g-1, respectively. And the adsorption process of MB and MV on PFPCS reached equilibrium within 20 min. Moreover, the adsorption conditions and mechanisms were investigated. The adsorption process was in good agreement with the pseudo-second-order and Langmuir isotherm models. The adsorption mechanism was also proposed to be electrostatic interaction and hydrogen bond. After six cycles of desorption-adsorption, the removal efficient of MB and MV could be kept above 95%. Thus, PFPCS was considered as a highly efficient absorbent for removing cationic dyes from polluted water due to excellent adsorption characteristics, low cost and environmental friendliness.

Chitosan/Zeolite Composite Aerogels for a Fast and Effective Removal of Both Anionic and Cationic Dyes from Water

Organic dyes are extensively used in many industrial sectors, and their uncontrolled disposal into wastewaters raises serious concerns for environmental and human health. Due to the large variety of such pollutants, an effective remediation strategy should be characterized by a broad-spectrum efficacy. A promising strategy is represented by the combination of different adsorbent materials with complementary functionalities to develop composite materials that are expected to remove different contaminants. In the present work, a broad-spectrum adsorbent was developed by embedding zeolite 13X powder (ZX) in a chitosan (CS) aerogel (1:1 by weight). The CS–ZX composite adsorbent removes both anionic (indigo carmine, IC) and cationic (methylene blue, MB) dyes effectively, with a maximum uptake capacity of 221 mg/g and 108 mg/g, respectively. In addition, the adsorption kinetics are rather fast, with equilibrium conditions attained in less than 2 h. The composite exhibits good mechanical properties in both dry and wet state, which enables its handling for reusability purposes. In this regard, preliminary tests show that the full restoration of the IC removal ability over three adsorption–desorption cycles is achieved using a 0.1 M NaOH aqueous solution, while a 1 M NaCl aqueous solution allows one to preserve >60% of the MB removal ability.

3D sponges of chemically functionalized chitosan for potential environmental pollution remediation: biosorbents for anionic dye adsorption and 'antibiotic-free' antibacterial activity

In this work, it was developed three-dimensional (3D) porous hydrogel sponges produced by the freeze-dried process using chitosan polymer functionalized by 11-mercaptoundecanoic acid (MUA). These chitosan-based sponges were used as cationic adsorbents for the removal of anionic methyl orange (MO) dye, simulating a model organic pollutant in aqueous medium. Moreover, these porous 3D constructs were also evaluated as 'antibiotic-free' antibacterial materials against gram-negative and gram-positive bacteria, Pseudomonas aeruginosa and Staphylococcus aureus, respectively, which were used as model pathogens possibly found in contaminated hospital discharges. These 3D hydrogels were comprehensively characterized through morphological methods such as scanning electron microscopy and X-ray micro-computed tomography techniques, combined with FTIR, Raman, and UV-visible spectroscopy analyses. Additionally, the surface area, the degree of swelling, and the adsorption profiles and kinetics of these scaffolds were systematically investigated. The chemically thiolated chitosan (CHI-MUA) hydrogels were successfully produced with a supramolecular polymeric network based on hydrogen bonds, disulfide bonds, and hydrophobic interactions that resulted in higher stability in aqueous medium than hydrogels of pristine chitosan. CHI-MUA exhibited sponge-like three-dimensional structures, with highly interconnected and hierarchical pore size distribution with high porosity and surface area. These architectural aspects of the 3D sponges favoured the high adsorption capacity for MO dye (∼388 mg.g^-1) in water with removal efficiency greater than 90% for MO solutions (from 20 mg.L^-1-1200 mg.L^-1). The adsorption data followed a pseudo-second-order kinetic model and adsorption isotherm analysis and spectroscopy studies suggested a multilayer behaviour with coexistence of adsorbent-adsorbate and adsorbate-adsorbate interactions. Additionally, the in vitro evaluation of toxicity (MTT and LIVE-DEAD® assays) of 3D-sponges revealed a non-toxic response and preliminary suitability for bio-related applications. Importantly, the 3D-sponges composed of chitosan-thiolated derivative proved high antibacterial activity, specificity against P. aeruginosa (model hazardous pathogen), equivalent to conventional antibiotic drugs, while no lethality against S. aureus (reference commensal bacteria) was observed.

Facet Engineering of Bismuth Molybdate via Confined Growth in a Nanoscale Template toward Water Remediation

Certain nanomaterials can filter and alter unwanted compounds due to a high surface area, surface reactivity, and microporous structure. Herein, γ-Bi₂MoO₆ particles are synthesized via a colloidal hydrothermal approach using organically modified Laponite as a template. This organically modified Laponite interlayer serves as a template promoting the growth of the bismuth molybdate crystals in the [010] direction to result in hybrid Laponite-Bi₂MoO₆ particles terminating predominantly in the {100} crystal facets. This resulted in an increase in particle size from lateral dimensions of <100 nm to micron scale and superior adsorption capacity compared to bismuth molybdate nanoparticles. These {100}-facet terminated particles can load both cationic and anionic dyes on their surfaces near-spontaneously and retain the photocatalytic properties of Bi₂MoO₆. Furthermore, dye-laden hybrid particles quickly sediment, rendering the task of particle recovery trivial. The adsorption of dyes is completed within minutes, and near-complete photocatalytic degradation of the adsorbed dye in visible light allowed recycling of these particles for multiple cycles of water decontamination. Their adsorption capacity, facile synthesis, good recycling performance, and increased product yield compared to pure bismuth molybdate make them promising materials for environmental remediation. Furthermore, this synthetic approach could be exploited for facet engineering in other Aurivillius-type perovskites and potentially other materials.