Ultrafast and efficient removal of Pb(II) from acidic aqueous solution using a novel polyvinyl alcohol superabsorbent

Engineering Bis-Pyridine N-Functionalized Cellulose Aerogel for Efficient Extraction of Cu2+ from High-Acidity Wastewaters: Coupling Molecular Scale Interpretation with Experiment

In order to address the issue of protonation of functional groups and structural instability on the surface of aerogel due to strong acidic wastewater, a three-dimensional bis-pyridine N cellulose aerogel [PEIPD/carboxymethyl cellulose (CMC)] with protonation resistance was prepared in this paper by grafting pyridine onto polyethylenimine. The adsorption capacity for Cu2+ of the as-prepared aerogel is as high as 1.64 mmol/g (pH 5) and is maintained well in high-acidity solutions (1.15 mmol/g at pH = 2). It reveals high selectivity, splendid anti-interference ability, and also reliable on the recycle performance. Through the zeta potential tests, this adsorbent reveals a rather low zero charge point (pHpzc = 2.2). The adsorption of Cu2+ on the adsorbent is consistent with the pseudo-second-order kinetic model and the Langmuir model, suggesting that the adsorption process is dominated by chemisorption in a monolayer. The characterizations by Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy proved pyridine N as responsible binding sites, based on which two possible mechanisms are proposed, including chelation and cation-π interaction. Density functional theory calculations are further used to precisely investigate the pathway. By comparing the binding energies, molecular electrostatic potentials, electron densities, and differential charge densities, the bis-pyridine N functional group is finally determined to be of much higher affinity to Cu2+ following chelation reaction as designated. By integrating bis-pyridine N with the CMC and understanding their crucial roles, this will provide significant insights into the rational design of aerogel adsorbents to enhance the recovery of Cu from strongly acidic wastewaters.

Research Advances in Superabsorbent Polymers

Superabsorbent polymers are new functional polymeric materials that can absorb and retain liquids thousands of times their masses. This paper reviews the synthesis and modification methods of different superabsorbent polymers, summarizes the processing methods for different forms of superabsorbent polymers, and organizes the applications and research progress of superabsorbent polymers in industrial, agricultural, and biomedical industries. Synthetic polymers like polyacrylic acid, polyacrylamide, polyacrylonitrile, and polyvinyl alcohol exhibit superior water absorption properties compared to natural polymers such as cellulose, chitosan, and starch, but they also do not degrade easily. Consequently, it is often necessary to modify synthetic polymers or graft superabsorbent functional groups onto natural polymers, and then crosslink them to balance the properties of material. Compared to the widely used superabsorbent nanoparticles, research on superabsorbent fibers and gels is on the rise, and they are particularly notable in biomedical fields like drug delivery, wound dressing, and tissue engineering.

Cellulose phosphonate/polyethyleneimine nano-porous composite remove toxic Pb(II) and Cu(II) from water in a short time

Current cellulose-based adsorbents suffer from the drawbacks of low adsorption capacity or slow adsorption rate for heavy metal ions. It is imperative to prepare new cellulose-based materials to improve the adsorption ability. In this work, we aim to introduce phosphonate groups to improve the adsorption ability of cellulose and select polyethyleneimine (PEI) for synergistic adsorption. A novel cellulose phosphonate/polyethyleneimine composite (MCCP-PEI) is prepared via the Mannich reaction. The structure and composition of MCCP-PEI are characterized by various advanced microscopy and spectroscopy techniques, and the results show that MCCP-PEI possesses abundant nano-porous structure, strong chelating sites, and excellent hydrophilicity. Besides, the adsorption behavior of MCCP-PEI for heavy metals has been systematically investigated. The results show that the adsorbent can quickly remove toxic Cu(II) and Pb(II) from water within 15 min and 20 min, respectively. The saturated adsorption capacity for Cu(II) and Pb(II) is 250.0 and 534.7 mg·g-1, respectively. X-ray photoelectron spectroscopy analysis combined with Density Functional Theory calculations reveal that the adsorption mechanism is chemical complexation and electrostatic attraction, and the phosphonate group plays a key role in the adsorption process.

Jute Stick-Derived Cellulose-Based Hydrogel: Synthesis, Characterization, and Methylene Blue Removal from Aqueous Solution

In this work, microcrystalline cellulose (MCC) was isolated from jute sticks and sodium carboxymethyl cellulose (Na-CMC) was synthesized from the isolated MCC. Na-CMC is an anionic derivative of microcrystalline cellulose. The microcrystalline cellulose-based hydrogel (MCCH) and Na-CMC-based hydrogel (Na-CMCH) were prepared by using epichlorohydrin (ECH) as a crosslinker by a chemical crosslinking method. The isolated MCC, synthesized Na-CMC, and corresponding hydrogels were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electronic microscopy (SEM), and energy dispersive spectroscopy (EDS) for functional groups, crystallinity, surface morphology, and composite elemental composition, respectively. Pseudo-first-order, pseudo-second-order, and Elovich models were used to investigate the adsorption kinetics. The pseudo-second-order one is favorable for both hydrogels. Freundlich, Langmuir, and Temkin adsorption isotherm models were investigated. MCCH follows the Freundlich model (R2 = 0.9967), and Na-CMCH follows the Langmuir isotherm model (R2 = 0.9974). The methylene blue (MB) dye adsorption capacities of ionic (Na-CMCH) and nonionic (MCCH) hydrogels in different contact times (up to 600 min), initial concentrations (10-50 ppm), and temperatures (298-318 K) were investigated and compared. The maximum adsorption capacity of MCCH and Na-CMCH was 23.73 and 196.46 mg/g, respectively, and the removal efficiency of MB was determined to be 26.93% for MCCH and 58.73% for Na-CMCH. The Na-CMCH efficiently removed the MB from aqueous solutions as well as spiked industrial wastewater. The Na-CMCH also remarkably efficiently reduced priority metal ions from an industrial effluent. An effort has been made to utilize inexpensive, readily available, and environmentally friendly waste materials (jute sticks) to synthesize valuable adsorbent materials.

Boosting interfacial solar steam generation by three-dimensional bilayer cellulose aerogels

Interfacial solar steam generation (ISSG) provides a sustainable approach of clean water production through desalination and water purification. It is still needed to pursue a fast evaporation rate, high-quality freshwater production, and low-cost evaporators. Herein, a three-dimensional (3D) bilayer aerogel was fabricated using cellulose nanofiber (CNF) as a skeleton filled with polyvinyl alcohol phosphate ester (PVAP), and carbon nanotubes (CNT) as a light absorbing material in the top layer. The CNF/PVAP/CNT aerogel (CPC) had broadband light absorption ability and exhibited an ultrafast water transfer rate. The lower thermal conductivity of CPC effectively confined the convert heat in the top surface and minimized heat loss. Additionally, a large amount of intermediate water caused by water activation decreased the evaporation enthalpy. Under 1 sun irradiation, the CPC-3 (3.0 cm height of CPC) achieved a high evaporation rate of 4.02 kg m-2 h-1 with an energy conversion efficiency of 125.1%. The additional convective flow and environmental energy made CPC achieve an ultrahigh evaporation rate of 11.37 kg m-2 h-1, surpassing 673% of the solar input energy. More importantly, the continuous solar desalination and higher evaporation rate (10.70 kg m-2 h-1) in seawater revealed that CPC was a promising candidate for practical desalination. Outdoor cumulative evaporation was up to 73.2 kg m-2 d-1 in weak sunlight and lower temperature, which would meet the daily drinking water demands of 20 people. The excellent cost-effectiveness of 1.085 L h-1 $-1 presented its potential for a wide range of practical applications, such as solar desalination, wastewater treatment, and metal extractions.

Study on Preparation of Chitosan/Polyvinyl Alcohol Aerogel with Graphene-Intercalated Attapulgite(GO-ATP@CS-PVA) and Adsorption Properties of Crystal Violet Dye

Adsorption is one of the effective methods of treating dye wastewater. However, the selection of suitable adsorbent materials is the key to treating dye wastewater. In this paper, GO-ATP was prepared by an intercalation method by inserting graphene oxide (GO) into the interlayer of alabaster attapulgite (ATP), and GO-ATP@CS-PVA aerogel was prepared by co-blending-crosslinking with chitosan (CS) and polyvinyl alcohol (PVA) for the adsorption and removal of crystalline violet dye from the solution. The physicochemical properties of the materials are characterized by various methods. The results showed that the layer spacing of the GO-ATP increased from 1.063 nm to 1.185 nm for the ATP, and the specific surface area was 187.65 m²·g^-1, which was 45.7% greater than that of the ATP. The FTIR results further confirmed the success of the GO-ATP intercalation modification. The thermogravimetric analysis (TGA) results show that the aerogel has good thermal stability properties. The results of static adsorption experiments show that at 302 K and pH 9.0, the adsorption capacity of the GO-ATP@CS-PVA aerogel is 136.06 mg·g^-1. The mass of the aerogel after adsorption-solution equilibrium is 11.4 times that of the initial mass, with excellent adsorption capacity. The quasi-secondary kinetic, Freundlich, and Temkin isotherm models can better describe the adsorption process of the aerogel. The biobased composite aerogel GO-ATP@CS-PVA has good swelling properties, a large specific surface area, easy collection and a low preparation cost. The good network structure gives it unique resilience. The incorporation of clay as a nano-filler can also improve the mechanical properties of the composite aerogel.

Heavy metal-contained wastewater in China: Discharge, management and treatment

A large amount of heavy metal-contained wastewater (HMW) was discharged during Chinese industry development, which has caused many environmental problems. This study reviewed discharge, management and treatment of HMW in China through collecting and analyzing data from China's official statistical yearbook, standards, technical specifications, government reports, case reports, and research paper. Results showed that industry wastewater discharged by an amount of about 221.6 × 10⁸ t (in 2012), where emission of heavy metals including Pb, Hg, Cd, Cr(VI), T-Cr was around 388.4 t (in 2012). Heavy metal emission with wastewater in east China and central south China was observed to be graver than that in other areas. However, control of heavy metals in Pb and Cd in northwest China was more difficult compared with other areas. In terms of management, China's government has issued many wastewater discharge standards, strict management policies for controlling HMW discharge in recent years, resulting in reduced HMW discharge. In addition, main HMW treatment technology in China was chemical precipitation, and other technologies such as membrane separation, adsorption, ion exchange, electrochemical and biological methods were also occasionally applied. In the future, chemical industries will be concentrated in northwest China, therefore control of HMW discharge should be paid much more attention in those areas. In addition, more effective and environment-friendly heavy metal removal and regeneration technologies should be developed, such as biomaterials adsorbent.

A sorbent containing pH-responsive chelating residues of aspartic and maleic acids for mitigation of toxic metal ions, cationic, and anionic dyes

t-Butyl hydroperoxide-initiated cycloterpolymerization of diallylaminoaspartic acid hydrochloride [(CH2[double bond, length as m-dash]CHCH2)2NH+CH(CO2H)CH2CO2H Cl-] (I), maleic acid (HO2CH[double bond, length as m-dash]CHCO2H) (II) and cross-linker tetraallylhexane-1,6-diamine dihydrochloride [(CH2[double bond, length as m-dash]CHCH2)2NH+(CH2)6NH+ (CH2CH[double bond, length as m-dash]CH2)2 2Cl-] (III) afforded a new pH-responsive resin (IV), loaded with four CO2H and a chelating motif of NH+⋯CO2 - in each repeating unit. The removal of cationic methylene blue (MB) (3000 ppm) at pH 7.25 and Pb(ii) (200 ppm) at pH 6 by IV at 298, 313, and 328 K followed second-order kinetics with E a of 33.4 and 40.7 kJ mol-1, respectively. Both MB and Pb(ii) were removed fast, accounting for 97.7% removal of MB within 15 min at 313 K and 94% of Pb(ii) removal within 1 min. The super-adsorbent resin gave respective q max values of 2609 mg g-1 and 873 mg g-1 for MB and Pb(ii). IV was also found to trap anionic dyes; it removed 91% Eriochrome Black T (EBT) from its 50 ppm solutions at pH 2. The resin was found to be effective in reducing priority metal contaminants (like Cr, Hg, Pb) in industrial wastewater to sub-ppb levels. The synthesis of the recyclable resin can be easily scaled up from inexpensive starting materials. The resin has been found to be better than many recently reported sorbents.

Phosphate-crosslinked β-cyclodextrin polymer for highly efficient removal of Pb(ii) from acidic wastewater

Novel phosphate-crosslinked β-cyclodextrin polymer was synthesized for highly efficient Pb(ii) removal from acidic wastewater.

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

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