Microwave-assisted synthesis of polyethylenimine-grafted nanocellulose with ultra-high adsorption capacity for lead and phosphate scavenging from water

Pomegranate peel adsorbents for water pollutants removal: preparation, characterization and applications

Pomegranate peel waste in the forms of raw biomass, biochar and activated carbon has been explored as adsorbents in water treatment. This review examined and discussed published works between 2008 and 2024 that focused on the utilization of pomegranate peel waste adsorbents with emphasis on preparation strategies, characterization techniques and applications. The thermal and chemical activation have shown to improve the structural and chemical properties of the resultant adsorbent materials to effectively adsorb various pollutants such as dyes, heavy metals, organics, inorganic nonmetals, and pharmaceuticals from water. The performance was compared and the avenues for future research was highlighted to shed insight into the potential of pomegranate peel adsorbents for environmental protection.

Three-dimensional, multi-functionalized nanocellulose/alginate hydrogel for efficient and selective phosphate scavenging: Optimization, performance, and in-depth mechanisms

Challenges in developing adsorbents with sufficient phosphate (P) adsorption capacity, selectivity, and regeneration properties remain to be addressed. Herein, a multi-functionalized high-capacity nanocellulose/alginate hydrogel (La-NCF/SA-PEI [La: lanthanum, NCF: nanocellulose fiber, SA: sodium alginate, PEI: polyethyleneimine]) was prepared through environmentally friendly methods. The La-NCF/SA-PEI hydrogel, featuring a 3D porous structure with interwoven functional groups (amino, quaternary ammonium, and lanthanum), demonstrated a maximum P adsorption capacity of 78.0 mg/g, exceeding most La-based hydrogel adsorbents. The kinetic and isotherm fitting results confirmed the multilayer chemisorption process. Comprehensive experimental results, instrumental analysis, and computational results revealed that the ammonium phosphate complex (NH3+-O-P) and the inner-sphere complex (La-O-P) formed by La(OH)3 dominated the selective P adsorption process. Density-functional theory (DFT) was employed to calculate the bond length between phosphate and each component of the La-NCF/SA-PEI. The calculation results revealed the double-bridge adsorption between the N (apex) atom on La-NCF/SA-PEI and the O (apex) atomic site in phosphate, including electrostatic adsorption and two hydrogen bonds (bond lengths 1.001 and 1.008 Å) between the O of PO43- and the H+ of the protonated amino group. Except the remarkable P adsorption performance (both municipal sewage and aquaculture tail water), the La-NCF/SA-PEI hydrogel's high selectivity toward P, environmental compatibility, and easy separability from water underscore its significant potential for phosphate-contaminated water remediation. The multi-functionalized La-NCF/SA-PEI demonstrate promising potential for P removal applications and advanced the development of sustainable, biomass-based adsorbents design.

Weak interaction strategy enables enhanced selectivity and reusability of arginine-functionalized imprinted aerogel for phosphate adsorption

Efficient phosphate adsorption from eutrophic waters remains challenging, fundamentally due to inherent trade-off in common adsorbents: high-binding energy between adsorbent and phosphate compromises reusability while low-binding energy suppresses selectivity. Herein, an innovative arginine-functionalized imprinted aerogel (AFIA-1:4) was fabricated by click chemistry and imprinting modification for overcoming this trade-off through synergistic weak interactions. Results shown that AFIA-1:4 exhibited high adsorption capacity (Qmax of 40.65 mg/g, 30.44 % higher than phoslock), rapid kinetics (15 min), and broad pH applicability (3-11) at 2 mg P/L solution. Moreover, its selectivity coefficient ranged from 10 to 90 even with 15- to 125-fold excess interfering anions, surpassing common adsorbents. After 10 cycles, AFIA-1:4 still maintained 98.15 % regeneration rate with 99.14 % phosphate desorption. Characterizations and calculations confirmed core roles of multiple hydrogen bonds and shape screening in maintaining selectivity and reusability. These findings advanced development of next-generation of phosphate adsorbents, which contributed to sustainable prevention and management of eutrophication.

One-step green synthesis of melamine-modified cellulose nanofiber composite aerogels for efficient removal of Pb(II) and Cu(II): Experiments and DFT calculations

A composite aerogel (CGMA) with high porosity (98.32 %) and multiple active sites was prepared for the adsorption of Pb(II) and Cu(II) by sol-gel combined with freeze-drying process using melamine and (3-Glycidyloxypropyl)trimethoxysilane as cellulose nanofiber modifying materials. Characterized by SEM-EDS, XPS, FTIR, BET, MIP and TG, CGMA has a hierarchical pore structure and abundant adsorption sites. At pH = 6, the adsorption reached equilibrium within 120 min, following the Pseudo second-order kinetic model and the Langmuir model, with maximum capacities of 268.1 mg/g for Pb(II) and 152.6 mg/g for Cu(II). The process was primarily governed by homogeneous chemisorption. The coexisting ion, organic matter, and water quality experiments confirmed the excellent anti-interference properties of CGMA. Competitive adsorption experiments showed that CGMA has excellent selective adsorption performance for Pb(II). After 5 cycles, Pb(II) and Cu(II) adsorption performance decreased to 79.21 % and 83.40 %, respectively. FTIR, XPS, DFT and RDG analysis showed that amino groups and oxygen-containing groups were the main sites of adsorption. CGMA forms coordination bonds and complexes with Pb(II) and Cu(II) via amine and oxygen groups and adsorbs via electron transfer, hydrogen bonding, and van der Waals forces, with Pb(II) being more selective. CGMA has good prospects for application in heavy metal ion treatment.

Inducement mechanism and control of self-acidification in elemental sulfur fluidizing bioreactor

The sulfur fluidizing bioreactor (S0FB) has significant superiorities in treating nitrate-rich wastewater. However, substantial self-acidification has been observed in engineering applications, resulting in frequent start-up failures. In this study, self-acidification was reproduced in a lab-scale S0FB. It was demonstrated that self-acidification was mainly induced by sulfur disproportionation process, accounting for 93.4 % of proton generation. Supplying sufficient alkalinity to both the influent (3000 mg/L) and the bulk (2000 mg/L) of S0FB was essential for achieving a successful start-up. Furthermore, the S0FB reached 10.3 kg-N/m3/d of nitrogen removal rate and 0.13 kg-PO43-/m3/d of phosphate removal rate, respectively, surpassing those of the documented sulfur packing bioreactors by 7-129 times and 26-65 times. This study offers a feasible and practical method to avoid self-acidification during restart of S0FB and highlights the considerable potential of S0FB in the treatment of nitrate-rich wastewater.

Functionalizing natural polymers to develop green adsorbents for wastewater treatment applications

The present study provides an overview of scientific developments made in the last decade in the field of green adsorbents focusing on the modifications in natural polymers and their applications such as, wastewater treatment, and ion exchange. For this purpose, an introduction to the various methods of modifying natural polymers is first given, and then the properties, application, and future priorities of green adsorbents are also discussed. Methods of modification of natural polymers under homogeneous and heterogeneous conditions using modifiers with different properties are also described. Various methods for modifying natural polymers and the use of the obtained green adsorbents are reviewed. A comparison of the sorption properties of green adsorbents based on natural polymers and other adsorbents used in industry has also been carried out. With the participation of green adsorbents based on natural polymers, the properties of treated wastewaters having toxic metal ions, organic dyes, petroleum products, and other harmful compounds was analyzed. Future perspectives on green adsorbents based on natural polymers are as also highlighted.

Graft onto approaches for nanocellulose-based advanced functional materials

The resurgence of cellulose as nano-dimensional 'nanocellulose' has unlocked a sustainable bioeconomy for the development of advanced functional biomaterials. Bestowed with multifunctional attributes, such as renewability and abundance of its source, biodegradability, biocompatibility, superior mechanical, optical, and rheological properties, tunable self-assembly and surface chemistry, nanocellulose presents exclusive opportunities for a wide range of novel applications. However, to alleviate its intrinsic hydrophilicity-related constraints surface functionalization is inevitably needed to foster various targeted applications. The abundant surface hydroxyl groups on nanocellulose offer opportunities for grafting small molecules or macromolecular entities using either a 'graft onto' or 'graft from' approach, resulting in materials with distinctive functionalities. Most of the reviews published to date extensively discussed 'graft from' modification approaches, however 'graft onto' approaches are not well discussed. Hence, this review aims to provide a comprehensive summary of 'graft onto' approaches. Furthermore, insight into some of the recently emerging applications of this grafted nanocellulose including advanced nanocomposite formulation, stimuli-responsive materials, bioimaging, sensing, biomedicine, packaging, and wastewater treatment has also been reviewed.

MOF-based stimuli-responsive controlled release nanopesticide: mini review

By releasing an adequate amount of active ingredients when triggered by environmental and biological factors, the nanopesticides that respond to stimuli can enhance the efficacy of pesticides and contribute to the betterment of both the environment and food safety. The versatile nature and highly porous structure of metal-organic frameworks (MOFs) have recently garnered significant interest as drug carriers for various applications. In recent years, there has been significant progress in the development of metal-organic frameworks as nanocarriers for pesticide applications. This review focuses on the advancements, challenges, and potential future enhancements in the design of metal-organic frameworks as nanocarriers in the field of pesticides. We explore the various stimuli-responsive metal-organic frameworks carriers, particularly focusing on zeolitic imidazolate framework-8 (ZIF-8), which have been successfully activated by external stimuli such as pH-responsive or multiple stimuli-responsive mechanisms. In conclusion, this paper presents the existing issues and future prospects of metal-organic frameworks-based nanopesticides with stimuli-responsive controlled release.

Cellulose Modified with Polyethylenimine (PEI) Using Microwave Methodology for Adsorption of Chromium from Aqueous Solutions

A large amount of agricultural waste was used to prepare cellulose (Cel) and then the surface was modified with PEI (Cel-PEI) using the microwave method. To be used as a metal adsorbent, the adsorption of Cr (VI) from an aqueous solution by Cel-PEI was measured using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) techniques. The parameters of Cr (VI) adsorption in solution by the Cel-PEI adsorbent were as follows: the pH of the solution was 3, the concentration of the chromium solution was 100 mg/L, and the adsorption time was 180 min at 30 °C using 0.01 g of adsorbent. Cel-PEI had a Cr (VI) adsorption capacity of 106.60 mg/g, while the unadjusted Cel was 23.40 mg/g and the material recovery showed a decrease in efficiency of 22.19% and 54.27% in the second and third cycles, respectively. The absorption isotherm of chromium adsorption was also observed. The Cel-PEI material conformed to the Langmuir model with an R² value of 0.9997. The kinetics of chromium adsorption showed that under pseudo-second-order analysis, with R² values of 0.9909 and 0.9958 for Cel and Cel-PEI materials, respectively. The G° and H° values of the adsorption process were negative, indicating that the adsorption is spontaneous and that the adsorption process is exothermic. The efficient preparation adsorbent materials for Cr (VI) was achieved using a short microwave method that is low-cost and environmentally friendly for use in the treatment of Cr-contaminated wastewater.

Efficient visual adsorption of Pb2+ by nanocellulose/sodium alginate microspheres with fluorescence sensitivity

In this study, carbon dots (CDs) were prepared by a one-pot hydrothermal method using tempo-oxidized cellulose nanocrystals (TOCNC) and polyethylenimine (PEI). The CDs were self-assembled with a microsphere adsorbent prepared using TOCNC and sodium alginate (SA). CDs-TOCNC/SA-an environmentally friendly, fluorescent-sensitive, and recyclable microsphere adsorbent-was obtained. FTIR analysis showed that PEI successfully modified the CDs. In addition, the fluorescence quenching of CDs was observed when the concentration of Pb²⁺ was 0.0001-100 mg/L, indicating that CDs can dynamically monitor Pb²⁺. CDs-TOCNC/SA can produce blue fluorescence under 365 nm UV light and selectively and efficiently adsorb Pb²⁺. When the concentration of Pb²⁺ was 0.0001-100 mg/L, fluorescence quenching of the adsorbent was observed, indicating that CDs-TOCNC/SA could visually adsorb Pb²⁺. The adsorption isotherm and kinetic parameters show that the adsorption process conforms to the Langmuir isotherm model at 298 K, and the maximum adsorption capacity of Pb²⁺ was 190.1 mg/g at pH = 5. Moreover, CDs-TOCNC/SA could still obtain 78.99 % Pb²⁺ after five sorption-desorption cycles. The adsorption mechanism may involve ion exchange, electrostatic attraction, intra-particle diffusion, and chemical complexation.

Polyethylenimine-grafted nitrogen-doping magnetic biochar for efficient Cr(VI) decontamination: Insights into synthesis and adsorption mechanisms

Herein, polyethylenimine (PEI)-grafted nitrogen (N)-doping magnetic biochar (PEI_MW@MNBC_BM) was synthesized, and characterization results showed that the microwave-assisted PEI grafting and ball milling-assisted N doping introduced abundant amino, pyridine N and pyrrole N structures onto biochar, which possessed high affinity to Cr(VI) in the anion form. The as-prepared PEI_MW@MNBC_BM displayed pH-dependence adsorption performance and high tolerance to co-existing ions with maximum uptake capacity of Cr(VI) identified as 183.02 mg/g. Furthermore, PEI_MW@MNBC_BM could bind Cr(VI) through electrostatic attraction, complexion, precipitation, reduction and pore filling. Especially, effective reduction of Cr(VI) was ascribed to cooperative electron transfer of partial oxygen-containing functional groups, intramolecular pyridine/pyrrole N, protonated amino and Fe²⁺ on the adsorbent, while oxygen-containing and amino functional groups from N-doping biochar and PEI synergistically complexed Cr(III) via providing lone pair electrons to form coordinate bonds. Furthermore, the stable precipitation was formed between Fe³⁺ and Cr(III). Additionally, the Cr(VI) elimination efficiency could maintain 95.83% even after four adsorption-desorption cycles, suggesting PEI_MW@MNBC_BM as a high-performance adsorbent for Cr(VI) contaminated water remediation.