Efficient and sustainable treatment of anionic dye wastewaters using porous cationic diatomite

Facile synthesis and ultrastrong adsorption of a novel polyacrylamide-modified diatomite/cerium alginate hybrid aerogel for anionic dyes from aqueous environment

An eco-friendly cationic polyacrylamide (CPAM)-modified diatomite/Ce(III)-crosslinked sodium alginate hybrid aerogel (CPAM-Dia/Ce-SA) was synthesized successfully and characterized by SEM-EDS, XRD, FTIR, UV-Vis and XPS. Adsorption performance, interaction mechanism and reusability of CPAM-Dia/Ce-SA used for the removal of acid blue 113 (AB 113), acid blue 80 (AB 80), acid yellow 117 (AY 117), Congo red (CR) and Direct Green 6 (DG 6) anionic dyes from aqueous media were investigated in detail. The results demonstrate that CPAM-Dia/Ce-SA aerogel is macroscopic polymer hybrid spheres with a particle size of around 1.3 mm, unique undulating mountain-like surface and porous mesostructure, and exhibits outstanding adsorption capacity for anionic dyes and good reusability. The maximum adsorption amounts of AB 113, AB 80, AY 117, CR and DG 6 by CPAM-Dia/Ce-SA were 3008, 1208, 914, 1832 and 1232 mg/g at pH 2.0, 60 min contact time and 25 °C, and corresponding removal efficiency reached individually 97.5, 96.6, 99.7, 99.9 and 98.5 % respectively and were less affected by increasing pH up to 10.0. Dye adsorption behaviour and adsorption processes with spontaneous and exothermic nature were perfectly interpreted by the Langmuir and Pseudo-second-order rate models respectively. Physicochemical and multisite-H-bonding synergies promoted the ultrastrong biosorption of anionic dyes by CPAM-Dia/Ce-SA.

Preparation of low-cost functionalized diatomite and its effective removal of ammonia nitrogen from wastewater

A low-cost functionalization method was used to treat diatomite, and an efficient adsorbent for ammonia nitrogen was prepared by optimizing the functionalization conditions. The functionalized diatomite (DTCA-Na) was characterized by SEM, EDS, BET, XRD, FT-IR, and TG. The results demonstrate that DTCA-Na has excellent adsorption performance after being modified with H2SO4 (60.00 wt.%), NaCl (5.00 wt.%), and calcination at 400 °C for 2 h. While studying the effect of adsorption factors on the removal of ammonia nitrogen, the kinetic and thermodynamic behaviors in the adsorption process were discussed. The removal efficiency of the simulated wastewater with the initial ammonia nitrogen concentration of 10.00 mg L-1 by the DTCA-Na was more than 80% when the contact time was 60 min, pH was 6-10, the dosage of adsorbent was 1.00 g, and the temperature was 25 °C. The adsorption process of ammonia nitrogen was conformed to the pseudo-first-order and Langmuir isothermal model. The removal efficiency of ammonia nitrogen was still above 80% after 5 times adsorption-desorption experiments. The DTCA-Na has a brighter prospect of application in the field of ammonia nitrogen wastewater treatment due to its excellent adsorption performance and low-cost advantage.

Super-efficient removal and adsorption mechanism of anionic dyes from water by magnetic amino acid-functionalized diatomite/yttrium alginate hybrid beads as an eco-friendly composite

The development of eco-friendly, large-capacity and easy-to-separate adsorbent materials has always been the focus and difficulty of adsorption technology in wastewater treatment applications based on the characteristics of dye wastewater. Therefore, in this study, a green magnetic glycine(Gly)-functionalized diatomite(Dia)/yttrium alginate (Y-SA) hybrid bead composite (Dia-Gly-Y-SA@Fe₃O₄) was synthesized by the droplet polymerization, and characterized by various modern analytical techniques. The adsorption performance and adsorption mechanism of the composite were evaluated and elucidated by the removal of anionic dyes direct Blue 106 (DB 106), Congo red (CR) and direct red 13 (DR 13) from water. The results show that the composite is a macroparticle gelpolymer with an average particle size of about 1.5 mm, flower-like fold surface structure, abundant porosity and sensitive magnetic response, and displays ultrastrong adsorption ability for three dyes. The adsorption equilibrium of each dye can be reached quickly within 30 min, and the removal efficiency is more than 95% at pH 2.0 and decreases slightly with pH up to 9.0. The adsorption processes could be explained by the Pseudo-second-order rate equation well. All isotherm data fitted the Langmuir model well, and the maximum adsorption capacities were 1635, 2359 and 1165 mg/g for DB 106, CR and DR 13 at 298 K, respectively. The ultrastrong adsorption performance was due to the multisite interaction of physicochemical action and various hydrogen bonds between hybrid beads and dye anions. As a cost-effective magnetic macroparticle adsorbent prepared by natural ingredients, Dia-Gly-Y-SA@Fe₃O₄ composite exhibits much more stronger adsorption efficiency, better collectability and no secondary pollution than powder Dia, and would have a good application prospect for the purification of anionic dye wastewater with a wide pH range.

Synthesis of Benzisothiazole-Azo Disperse Dyes for High Resistance to Alkaline Treatments and Peroxide Bleaching of Polyester and Polyester/Cotton Fabric

We proposed in this paper to design and synthesize a series of benzisothiazole-based heterocyclic azo disperse dyes with high resistance to alkali and peroxide. These newly synthesized disperse dyes were confirmed using ¹H nuclear magnetic resonance (¹H NMR), mass spectroscopy, and a UV-visible spectrophotometer. The resistances to alkali and peroxide were examined by dyeing polyester fabric with these synthesized disperse dyes in sodium hydroxide solution and alkaline hydrogen peroxide solution, respectively. It was found that the disperse dyes having cyano and hydroxyl groups exhibited poor resistance to alkali and peroxide. When the cyano and hydroxyl groups were substituted with ethyl, benzyl, and p-methylbenzyl groups, the synthesized disperse dyes exhibited extremely high resistance to alkali and peroxide. Utilizing the high resistance to alkali and peroxide of synthesized disperse dyes, the polyester suede fabric and polyester/cotton blended fabric could be produced by combining pretreatment with dyeing in one bath. From pilot-plant production based on 1-ton fabric, the one-bath process provided the advantages of saving electric power, steam, water, and man-hour.

Preparation of Adsorbent Based on Polyacrylate Latex Solid Waste and Its Application in the Treatment of Dye Wastewater

It is a great challenge to sustainably produce and apply water-based coatings and inks in terms of realizing the green resource utilization of polyacrylate latex solid waste (PLSW) and avoid its secondary pollution. In this paper, a kind of high value-added amphoteric ion-exchange resin (AIER) was prepared by using diethylenetriamine to amidate PLSW under the optimized conditions from a Box-Behnken design. Its adsorption and regeneration properties and the universality of the method were investigated. The results suggested that AIER possessed a high removal efficiency to anionic dyes, and the batch dye adsorption processes were endothermic and spontaneous, which is consistent with a pseudo-second-order kinetic model. The penetration adsorption capacities of AIER were recorded to be 987.08 mg/g for RR239 and 1037.75 mg/g for RB5 at the optimized operating conditions of column height = 6.4 cm, flow rate = 1 mL/min, and dye solution of 500 mg/L. They were more than 200 times larger than that of commercial activated carbon when the mixture composed of AIER particle and diatomite particle (filter aid agent) was used as a fixed-bed adsorbent. Zeta potential analysis results indicated that the good adsorption and regeneration performances of AIER were mainly attributed to the presence of amino and carboxyl groups in the molecular structure of AIER. Most importantly, this method possessed excellent practicability and universality for different types of PLSW from factory wastewater. The results provide a feasible method and theoretical basis for the green resource utilization of PLSW, and the goal of "waste control by waste" was fundamentally achieved.

Preparation of Magnetic Composite Polyaniline/Fe3O4−Hydrotalcite and Performance in Removal of Methyl Orange

Magnetic composite fabricated from polyaniline and Fe3O4-hydrotalcite (Pan/MHT) was successfully applicated for removal of methyl orange (MO) from wastewater. The structure and properties of Pan/MHT were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, vibrating sample magnetometer, and Brunauer-Emmett-Teller adsorption isotherm. Adsorption kinetic results indicated that the adsorption process followed pseudosecond-order kinetic model ( $R^2=0.999$ ), MO adsorption onto Pan/MHT was well described by Freundlich isotherm ( $R^2=0.994$ ), and the MO adsorption capacity of 2 Pan/MHT obtained the highest with $Q_e=156.25\text{mg}/\text{g}$ . Batch adsorption experiments were carried out using magnetic composite with the effects of initial MO concentration, solution pH, and adsorbent dosage. The results revealed that the magnetic Pan/MHT exhibited efficient adsorption of MO in the aqueous solution as a result of the affinity for organic dyes, microporous structure, and suitable surface area for adsorption (15,460 m2/g). The superparamagnetic behavior of Pan/MHT (with $H_c=18.56\text{Oe}$ , $M_s=23.38\times {10}^{-3}\text{emu}/\text{g}$ , and $M_r=0.91\times {10}^{-3}\text{emu}/\text{g}$ ) helps that it could be separated from the solution and performs as an economical and alternative adsorbent to removal and degrade azo dye from wastewater. Pan/MHT was also investigated to reuse after desorption of MO in 0.1 M HCl, and the results show that 2 Pan/MHT can be reused for 4 cycles with $Q_e=79.66\text{mg}/\text{g}.$

Facile and scalable preparation of ZIF-67 decorated cotton fibers as recoverable and efficient adsorbents for removal of malachite green

Recently, metal–organic frameworks (MOFs) have received considerable attention as highly efficient adsorbents for dye wastewater remediation. However, the immobilization of MOFs on the substrate surfaces to fabricate easy recyclable adsorbents via a facile route is still a challenge. In this work, ZIF-67/cotton fibers as adsorbents for dye removal were prepared in a large-scale using a simple coordination replication method. The successful fabrication of the ZIF-67/cotton fibers was confirmed by FTIR, XRD, XPS, SEM and BET analysis, respectively. As expected, the as-prepared ZIF-67/cotton fibers exhibited high adsorption capacity of 3787 mg/g towards malachite green (MG). Meanwhile, the adsorption kinetics and isotherm obeyed the pseudo-second-order kinetics and Langmuir model, respectively. Moreover, its removal efficiency towards MG was not significantly influenced by the pH and ionic strength of aqueous solution. Most importantly, the ZIF-67/cotton fibers can remove MG from synthetic effluents, and it can be easily regenerated without filtration or centrifugation processes, with the regeneration efficiency remaining over 90% even after 10 cycles. Additionally, the ZIF-67/cotton fibers presented excellent antimicrobial performance against E. coli and S. aureus. Hence, the distinctive features of the as-prepared ZIF-67/cotton fibers make it promisingly applicable for the colored wastewater treatment.

Surface Modification of Attapulgite by Grafting Cationic Polymers for Treating Dye Wastewaters

In this study, the cationic polymer poly-epichlorohydrin-dimethylamine was immobilized on natural attapulgite to improve the dye adsorption capacities. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, nitrogen adsorption-desorption isotherms, scanning electron microscope (SEM) analysis, zeta potential analysis, and particle size analysis were used to determine the characteristics of modified attapulgite. Results showed that the poly-epichlorohydrin-dimethylamine had been successfully grafted onto the surface of attapulgite without altering its crystal structure. After cationic modification, the specific surface area of attapulgite obviously decreased, and its surface zeta potentials possessed positive values in the pH range from 3 to 11. The cation-modified attapulgite displayed high adsorption capacities for anionic dyes, and its maximum adsorption capacities were 237.4 mg/g for Reactive Black 5 and 228.3 mg/g for Reactive Red 239; this is corroborated by Langmuir’s isotherm studies. It was demonstrated that the two reactive dyes could be 100% removed from effluents when cation-modified attapulgite was used in column operation modes. Its treatment capacities were more than three times larger than that of activated carbon. The regeneration study verified better utilization and stability of the fabricated adsorbent in column operation. This work has conclusively confirmed the potential of the new modified attapulgite for effectively treating dye wastewaters.