Synthesis of Three-Dimensional Hierarchical Flower-Like Mg–Al Layered Double Hydroxides with Excellent Adsorption Performance for Organic Anionic Dyes

In this work,a facile and effective strategy to prepare three-dimensional(3D)hierarchical flower-like Mg–Al layered double hydroxides(3D-LDH)was developed via a one-step double-drop coprecipitation method usingγ-Al 2O 3particles as a template.The characterization and experimental results showed that the calcined product,3D-LDO,features a large specific surface area of 204.2 m^(2)/g,abundant active sites,and excellent adsorption performance for Congo red(CR),methyl orange(MO),and methyl blue(MB).The maximum adsorption capacities of 3D-LDO for CR,MO,and MB were 1428.6,476.2,and 1666.7 mg/g,respectively;such performance is superior to that of most reported adsorbents.The adsorption mechanism of organic anionic dyes by 3D-LDO was extensively investigated and attributed to surface adsorption,the memory effect of 3D-LDO,and the unique 3D hierarchical flower-like structure of the adsorbent.Recycling performance tests revealed that3D-LDO has satisfactory reusability for the three organic anionic dyes.

Preparation and Formation Mechanism of Porous Polyurea by Reaction of Toluene Diisocyanate with Water and Its Application as Adsorbent for Anionic Dye Removal

A novel and easy one-step protocol for preparation of a new porous material, polyurea （PPU）, is reported, which is accomplished through a precipitation polymerization of toluene diisocyanate （TDI） in mixed solvent of H20-acetone without need for surfactant and porogen. Effects of TDI concentration, mechanical stirring, solvent composition and TDI addition rate on PPU structure are studied. Surface morphology and pore structure of PPU are characterized by scanning electron microscopy and Hg intrusion. Chemical structure of the PPU polymer is investigated using NMR, XRD and FTIR. Mechanism of pore formation is discussed. The obtained PPU is used as adsorbent for anionic dyes adsorption investigation. Two anionic dyes, remazol brilliant blue R and acid fuchsine, are tested. The results indicate that the as-prepared PPU is of high performance in dye adsorption and recycled use. This study provided therefore a facile route to the preparation of a novel and attractive adsorbent candidate for removal of anionic dyes from wastewaters.

Evaluation of antioxidant enzymes activities and identification of intermediate products during phytoremediation of an anionic dye(C.I. Acid Blue 92) by pennywort(Hydrocotyle vulgaris)

The potential of pennywort （Hydrocotyle vulgaris） for phytoremediation of C.I. Acid Blue 92 （AB92） was evaluated. The effects of various experimental parameters including pH, temperature, dye concentration and plant weight on dye removal efficiency were investigated. The results showed that the optimal condition for dye removal were pH 3.5 and temperature 25~C. Moreover, the absolute dye removal enhanced with increase in the initial dye concentration and plant weight. Pennywort showed the same removal efficiency in repeated experiments （four runs） as that obtained from the first run （a 6-day period）. Therefore, the ability of the plant in consecutive removal of AB92 confirmed the biodegradation process. Accordingly, a number of produced intermediate compounds were identified. The effect of treatment on photosynthesis and antioxidant defense system including superoxide dismutase, peroxidase and catalase in plant roots and leaves were evaluated. The results revealed a reduction in photosynthetic pigments content under dye treatments. Antioxidant enzyme responses showed marked variations with respect to the plant organ and dye concentration in the liquid medium. Overall, the increase in antioxidant enzyme activity under AB92 stress in the roots was much higher than that in the leaves. Nevertheless, no significant increase in malondialdehyde content was detected in roots or leaves, implying that the high efficiency of antioxidant system in the elimination of reactive oxygen species. Based on these results, pennywort was founded to be a capable species for phytoremediation of AB92-contaminated water, may be effective for phytoremediation dye-contaminated polluted aquatic ecosystems.

A new fast swelling poly[DAPB-co-DMAAm-co-AASS] superabsorbent hydrogel for removal of anionic dyes from water

The objective of this research is to utilize a new poly[N,N-diallyl pyrrolidinium bromide-co-N,Ndimethyl acrylamide-co-acrylic acid sodium salt]superabsorbent hydrogel（SAH）for the removal of two anionic dyes,e.g.,Reactive Red 5B（RR5B）and Reactive Orange M2R（ROM2R）,from water.The SAH was characterized by swelling in water,FTIR,TGA and SEM.The SAH DDA6showed good swelling property and thermal stability.We have also investigated the parameters affecting dye adsorption such as pH,adsorbent dose,adsorption rate and initial dye concentration.The experimental data were also analyzed by applying the well known Langmuir and Freundlich isotherm models.

Separation/degradation behavior and mechanism for cationic/anionic dyes by Ag-functionalized Fe_(3)O_(4)-PDA core-shell adsorbents

High-performance adsorbents have been well-studied for the removal of organic dye pollutants to promote environment remediation.In this study,an Ag nanoparticle-functionalized Fe_(3)O_(4)-PDA nanocomposite adsorbent(PDA-Fe_(3)O_(4)-Ag)was synthesized,and the adsorption/separation performance of commonly used cationic and anionic organic dyes by the PDA-Fe_(3)O_(4)-Ag adsorbent were assessed.Overall,PDA-Fe_(3)O_(4)-Ag exhibited a significantly higher adsorption capacity for cationic dyes compared to anionic dyes,the highest of which was more than 110.0 mg/g(methylene blue(MB)),which was much higher than not only the adsorption capacities of the anionic dyes in this study but also other dye adsorption capacities reported in the literature.The dye adsorption kinetics data fitted well to both the pseudo second-order kinetics model and the Langmuir isotherm model,suggesting a monolayer-chemisorption-dominated adsorption mode.Thermodynamics analysis indicated that the adsorption process was both endothermic and spontaneous.Furthermore,the PDAFe_(3)O_(4)-Ag adsorbent achieved high photodegradation removal rates of the dyes,especially neutral red(NR)and methyl orange(MO),which were 91.2%and 87.5%,respectively.With the addition of PDA-Fe_(3)O_(4)-Ag,the degradation rate constants of NR and MO increased from 0.08×10^(−2)and 0 min^(−1)to 2.11×10^(−2)and 1.73×10^(−2)min−1,respectively.The high adsorption and photocatalytic degradation performance of the PDA-Fe_(3)O_(4)-Ag adsorbent make it an excellent candidate for removing cationic and anionic dyes from the industrial effluents.

Preparation of a Novel Acid Doped Polyaniline Adsorbent for Removal of Anionic Pollutant from Wastewater

Polyaniline(PANI) was one of the most extensively studied adsorbents due to its low cost and good environmental stability. The objective of the current study was to improve the selective capabilities of PANI for anionic dyes. We found that the acid doped PANI prepared with hydrochloric acid and p-toluenesulfonic acid(PTSA) could selectively adsorb anionic dyes. It exhibited very good selectivity for OG dye, the mechanism was proposed based on the chemical interaction of PANI with the sulfonate group of the dyes. The effects of solution p H, initial dye concentration, and different HCl/PTSA mole ratios on the adsorption capacity of OG have been investigated. Kinetic simulations indicated that the adsorption process could be well represented by pseudo-second-order kinetic plots. The isothermal adsorption curve fitting also showed that the adsorption process could be well described by the Langmuir isothermal equation. The results showed that acid doped PANI could be employed as a promising adsorbent for anion removal from dye wastewater.

Preparation of Fe-Mg MOFs and Its Application in Removal of RhB and MO

The world wide application of dyes in papermaking, fabric, lithography, leather and other industrial production, has attracted more attention, due to water pollution caused by these organic dyes. Metal-organic frameworks (MOFs) which are a physical adsorption method of wastewater treatment are a kind of special three-dimensional crystal-like constituents built by multipurpose ligands and metallic ion classes, showing an advantage in removal of pollutants from solutions because of its unique properties are convenient for operation, high removal efficiency, and low cost. In this study, we investigated Fe-Mg based metal organic framework, Fe-Mg MOFs which was directly synthesized by the hydrothermal method. The obtained materials were analyzed with XRD, FT-IR, TG-DTG, SEM etc. and used for the treatment of printing and dyeing wastewater. The results showed that it has good adsorption performance for cation dye rhodamine B (RhB) and anion dye methyl orange (MO) in a wide pH range. The Fe-Mg MOF even after the 4th run, the Fe-Mg MOF catalyst still maintained nearly the initial catalytic activities. The kinetic studies revealed the adsorption process of the both contaminants obeys a pseudo-second order model. In addition, the equilibrium adsorption data of RhB and MO are in good agreement with Langmuir models. The maximum adsorption capacities are 694.44 and 236.97 mg/g at 308 K respectively. This work synthesizes a promising dual-functional adsorbent that can remove cationic and anionic dyes, which provide potential applications for actual wastewater treatment.

A cationic metal-organic framework based on {Zn4} cluster for rapid and selective adsorption of dyes

Until now, to remove the harmful organic dyes from effluents is an outstanding challenge. The design and synthesis of new porous materials capable of selectively adsorbing dyes are critical to the environment and human health. Here, a unique cluster-based cationic metal-organic framework, named{[Zn8（BTA）6（L）5Cl2]·（NO3）3}·5 DMF（NUM-4） was synthesized, which displays one-dimensional（1 D）open channels along a axis in its 3 D supramolecular stacking structure. Benefiting from the nature of cationic framework and high surface area/pore volume, NUM-4 shows rapid and selective adsorption of anionic dyes（MO, AO, CR and MB） based on the charge-exclusive effect. Besides, the adsorbed dyes can be easily released in NH4Cl saturated solution of ethanol.

Preparation and assistant-dyeing of formaldehyde-free amphoteric acrylic retanning agent

With the enhancement of environmental protection consciousness,concerns have been raised about non-toxic and biodegradable leather retanning agents.According to the European standard 2002/231/EC,the free formaldehyde content of leather products should be less than 150 mg/kg.As one of the retanning agents in the market,the content of free formaldehyde in the Multifunctional retanning agent(MTA)is 372.22 mg/kg and higher than the limit value.In this work,glutaraldehyde as an alternative of formaldehyde was used to modify acrylic polymer and an amphoteric acrylic retanning agent was prepared.Then it was used in retanning process,and its retanning and assistant-dyeing properties were investigated.The results showed that the free formaldehyde content of amphoteric acrylic retanning agent modified with glutaraldehyde was only 4.17mg/kg.Meanwhile,the presence of amino groups in the amphoteric acrylic retanning agent improved the dyeing properties of leather by electrostatic attraction.Compared with the leather treated with anionic acrylic retanning agent,the residual dye concentration of the dyeing effluent of the retanned leather with amphoteric acrylic retanning agent decreased from 17.4mg/L to 10.0mg/L,and the dyed leather had better resistances to friction and water-washing.In addition,the BOD 5/COD value of the wastewater after Mannich base polymer retanning was only 0.32,indicating that the retanning agent was biodegradable.Moreover,the leather retanned with amphoteric acrylic retanning agent had good thermal stability,fullness and physical and mechanical properties.

Preparation and properties of chitosan–metal complex：Some factors influencing the adsorption capacity for dyes in aqueous solution

Chitosan–metal complexes have been widely studied in wastewater treatment, but there are still various factors in complex preparation which are collectively responsible for improving the adsorption capacity need to be further studied. Thus, this study investigates the factors affecting the adsorption ability of chitosan–metal complex adsorbents, including various kinds of metal centers, different metal salts and crosslinking degree. The results show that the chitosan–Fe（ Ⅲ） complex prepared by sulfate salts exhibited the best adsorption efficiency（100%） for various dyes in very short time duration（10 min）, and its maximum adsorption capacity achieved 349.22 mg/g. The anion of the metal salt which was used in preparation played an important role to enhance the adsorption ability of chitosan–metal complex. SO4^（2-） ions not only had the effect of crosslinking through electrostatic interaction with amine group of chitosan polymer, but also could facilitate the chelation of metal ions with chitosan polymer during the synthesis process.Additionally, the p H sensitivity and the sensitivity of ionic environment for chitosan–metal complex were analyzed. We hope that these factors affecting the adsorption of the chitosan–metal complex can help not only in optimizing its use but also in designing new chitosan–metal based complexes.