Urea functionalization of ultrasound-treated biochar: A feasible strategy for enhancing heavy metal adsorption capacity

The main objective of a series of our researches is to develop a novel acoustic-based method for activation of biochar. This study investigates the capability of biochar in adsorbing Ni(II) as a hazardous contaminant and aims at enhancing its adsorption capacity by the addition of extra nitrogen and most probably phosphorous and oxygen containing sites using an ultrasono-chemical modification mechanism. To reach this objective, biochar physically modified by low-frequency ultrasound waves (USB) was chemically treated by phosphoric acid (H₃PO₄) and then functionalized by urea (CO(NH₂)₂). Cavitation induced by ultrasound waves exfoliates and breaks apart the regular shape of graphitic oxide layers of biochar, cleans smooth surfaces, and increases the porosity and permeability of biochar's carbonaceous structure. These phenomena synergistically combined with urea functionalization to attach the amine groups onto the biochar surface and remarkably increased the adsorption of Ni(II). It was found that the modified biochar could remove > 99% of 100 mg Ni(II)/L in only six hours, while the raw biochar removed only 73.5% of Ni(II) in twelve hours. It should be noted that physical treatment of biochar with ultrasound energy, which can be applied at room temperature for a very short duration, followed by chemical functionalization is an economical and efficient method of biochar modification compared with traditional methods, which are usually applied in a very severe temperature (>873 K) for a long duration. Such modified biochars can help protect human health from metal-ion corrosion of degrading piping in cities with aging infrastructure.

Phenol adsorption and desorption with physically and chemically tailored porous polymers: Mechanistic variability associated with hyper-cross-linking and amination

Understanding phenol adsorption-desorption mechanisms allows adsorbent tailoring to improve capacity and adsorbent reuse. Amberlite™ XAD4, a commercial styrenic polymer that is convenient to physically and chemically modify, was functionalized with dimethylamine (DMA) or trimethylamine (TMA) and/or hyper-cross-linked with 1,2-dichloroethane. These modifications were applied to enhance individual and/or synergistic phenol adsorption mechanisms, including hydrogen bonding, electrostatic interactions, and π-π dispersion forces. While XAD4-DMA adsorbs more phenol at pH = 6, XAD4-TMA has 23% higher capacity at pH = 11 due to adsorbate deprotonation that increases electrostatic interactions. Combining hyper-cross-linking with amination maximizes adsorption capacity due to synergistic impacts associated with increased micropore volume and surface affinity. Amine groups reduce desorption efficiency by 6-94% due to stronger adsorbate-adsorbent interactions compared to π-π dispersion forces. Isobutanol, which forms hydrogen bonds, is the most efficient desorption solvent, followed by chloroform, which has the same polarity index but does not hydrogen bond. n-Hexane only desorbs phenol removed with π-π dispersion forces and is not appropriate to regenerate aminated polymers. 0.1 N NaOH is an environmentally benign solvent for regenerating as-received XAD4 and XAD4-DMA, but not XAD4-TMA. Understanding phenol adsorption mechanisms allows development of physiochemically modified polymers with increased phenol adsorption capacity and regeneration efficiency.

Translation of a solution-based biomineralization concept into a carrier-based delivery system via the use of expanded-pore mesoporous silica

Mineralization of collagen fibrils using solution-based systems containing biomimetic analogs of matrix proteins to stabilize supersaturated calcium phosphate solutions have been predictably achieved in vitro. Solution-based systems have limitations when used for in-situ remineralization of human hypomineralized tissues because periodic replenishment of the mineralizing solution is infeasible. A carrier-based platform designed for delivering mineral precursors would be highly desirable. In the present work, mesoporous silica nanoparticles with expanded pores (eMSN; 14.8nm) were synthesized. Polyacrylic acid-stabilized amorphous calcium phosphate (PA-ACP) was generated from a supersaturated calcium and phosphate ion-containing solution, and chosen as the model mineralizing phase. After amine functionalization (AF) of the eMSN through a post-grafting method, the positively-charged AF-eMSN enabled loading of PA-ACP by electrostatic interaction. In-vitro cytotoxicity testing indicated that PA-ACP@AF-eMSN was highly biocompatible. The release kinetics of mineralization precursors from PA-ACP@AF-eMSN was characterized by an initial period of rapid calcium and phosphate release that reached a plateau after 120h. Intrafibrillar mineralization was examined using a 2-D fibrillar collagen model; successful mineralization was confirmed using transmission electron microscopy. To date, this is the first endeavor that employs expanded-pore mesoporous silica to deliver polymer-stabilized intermediate precursors of calcium phosphate for intrafibrillar mineralization of collagen. The carrier-based delivery system bridges the gap between contemporary solution-based biomineralization concepts and clinical practice, and is useful for in-situ remineralization of bone and teeth.

STATEMENT OF SIGNIFICANCE

Concepts of collagen biomineralization have been reasonably well established in the past few years and intrafibrillar mineralization of collagen fibrils can be predictably achieved with analogs of matrix proteins using solution-based systems. However, solution-based systems have their limitations in clinical applications that require direct application of mineralization precursors in-situ because periodic replenishment of the mineralizing solution is impossible. The present work presents for the first time, the use of amine-functionalized mesoporous silica with expanded pores for loading and release of polyacid-stabilized amorphous calcium phosphate mineralization precursors, and for intrafibrillar mineralization of type I collagen fibrils. This strategy represents an important step in the translational application of contemporary biomineralization concepts for in-situ remineralization of bone and teeth.

Removal of As(V), Cr(VI) and Cu(II) using novel amine functionalized composite nanofiltration membranes fabricated on ceramic tubular substrate

Novel amine functionalized composite membranes were prepared over tubular ceramic substrate using facile dip-coating and cross-flow filtration approach. The two fabricated membranes, P-60S and P-60S-EDTA with polyethyleneimine (PEI) and EDTA-modified PEI as functional layers respectively, were characterized in terms of EDX, FTIR, XPS, FESEM, AFM and contact angle analyses which confirmed their stable physical and chemical structure for use in high pressure application. Clean water permeability and MWCO study revealed the superior permeability and rejection efficiency of the P-60S-EDTA compared to the P-60S membrane. Incorporation of bulky EDTA molecules in the membrane functional layer simultaneously decreased pore size and increased membrane hydrophilicity. The removal of As(V), Cr(VI) and Cu(II) heavy metals by both membranes were found to be highly pH dependent and overall rejection improved in case of P-60S-EDTA membrane [99.82% for Cu(II), 96.75% for As(V) and 97.22% for Cr(VI)]. Interestingly, rejection of As(V) and Cr(VI) was significantly improved in presence of Cu(II) due to volume resistance provided by EDTA-Cu(II) complex towards the passage of other heavy metal ions. Excellent stability of P-60S-EDTA membrane in continuous operation of 36 h in both ideal and practical water environment suggests its promising application in real field heavy metal contaminated waste water treatment.

Modification of multi-walled carbon nanotubes by 1,3-diaminopropane to increase CO2 adsorption capacity

Greenhouse gas emissions have increased dramatically over the past years and had a significant impact on global warming. This study investigates the modification of multi-walled carbon nanotubes (MWCNTs) with diamine precursor to improve the carbon dioxide adsorption capacity. To achieve this goal, pristine multi-walled CNTs were functionalized in a two-step process. In the first step, multi-walled carbon nanotubes were functionalized with a mixture of diluted sulfuric and nitric acid (5 M HNO₃/5 M H₂SO₄ with a volume ratio of 1:3) to sequestrate catalytic metal particles and oxidation of MWCNTs. In the second step, oxidized carbon nanotubes were functionalized with 1,3-diaminopropane (DAP) solution to improve the performance of multi-walled CNT in the carbon dioxide adsorption process. Specifications and characteristics of raw and modified carbon nanotubes were determined using FTIR, SEM, TGA, XRD, and N₂ adsorption-desorption isotherms at 77 K. The CO₂ adsorption capacity was measured at 303-323 K and pressures up to 17.3 bar using volumetric method. At 303 K and pressure of 17.3 bar, 92.71 mg g^-1 of CO₂ was adsorbed on MWCNT/DAP, while the CO₂ uptake of raw MWCNT in similar conditions was just 48.49 mg g^-1. The results revealed that amine groups attached to the carbonaceous surfaces during the functionalization process cause the formation of carbon dioxide-adsorption sites on multi-walled CNTs which increased the adsorption capacity of MWCNTs. Experimental data was modeled with Langmuir and Freundlich adsorption isotherms and concluded that the Freundlich model has more fitness with the experimental data.

Kinetics and mechanism of efficient removal of Cu(II) ions from aqueous solutions using ethylenediamine functionalized cellulose sponge

The present work elucidates achieving superior Cu(II) adsorption capacity using a facile protocol and a biodegradable material. Copper is one of the most prevalent metals used in industries, which creates severe health effects to the human and aquatic lives when present in excess. Cellulose sponge (CS) used as kitchen wipe was chosen and amine functionalities were introduced on it using ethylenediamine. Potentiality of the amine functionalized cellulose sponge (AF-CS) in Cu(II) removal is investigated for the first time. The batch adsorption parameters were optimized and various nonlinear kinetic and isotherm models were elaborately studied. The adsorption using CS and AF-CS behaved under a pseudo-second-order model and followed chemisorption. The maximum adsorption capacity values using AF-CS and CS from the Langmuir isotherm model were calculated to be 596.96 mg/g and 230.63 mg/g, respectively. Thence, AF-CS possesses proportionately higher adsorption capacity in comparison with CS due to the insertion of -NH₂ groups. Further, the mechanism involved in the adsorption process was explored in detail through FESEM, FT-IR, FT-Raman and TGA analysis. The AF-CS sponge was stable on repeated use and retained 90% efficiency at the end of the 10th cycle. A highly effective, easily recyclable, biodegradable and cost-effective adsorbent has been synthesized possessing an extraordinarily high adsorption capacity towards Cu(II) ions.

Improving hydraulic permeability, mechanical properties, and chemical functionality of cellulose acetate-based membranes by co-polymerization with tetraethyl orthosilicate and 3-(aminopropyl)triethoxysilane

Composite cellulose acetate (CA) membranes are widely used but their multiphase nature results in additive losses, poor mechanical strength, low chemical resistance and thermal stability, limiting their separation/purification yields. To overcome this, we fabricated monophasic hybrid membranes using a modified phase inversion technique, where tetraethylorthosilicate and 3-(aminopropyl)triethoxysilane were added to the CA casting solution. The resulting co-polymerization between CA, silanols and amine-functionalized silica groups, through sol-gel chemistry, was proved by ATR-FTIR (1118 cm^-1, ν(SiOC)). The presence of propyl-amine groups increases the hydraulic permeability (3×), the rupture elongation (×1.5), and decreases the Young modulus (×1/2), due to the disruption of the CA-silica 3D network. For high propyl-amine contents this behaviour is reversed due to intensive cross-linking between CA-silica chains (decrease in 903 cm^-1, ν(CH₃COOC-)). The addition of silica- and amine-based structures to the CA framework increases the system degrees of freedom, opening the door to the design of new CA membranes.

Interfacial molecular regulation of TiO2 for enhanced and stable cocatalyst-free photocatalytic hydrogen production

On the basis of the inherent property limitations of commercial P25-TiO₂, many surface interface modification methods have attracted substantial attention for further improving the photocatalytic properties. However, current strategies for designing and modifying efficient photocatalysts (which exhibit complicated manufacturing processes and harsh conditions) are not efficient for production that is low cost, is nontoxic, and exhibits good stability; and therefore restrict practical applications. Herein, a facile and reliable method is reported for in situ amine-containing silane coupling agent functionalization of commercial P25-TiO₂ by covalent surface modification for constructing a highly efficient photocatalyst. As a consequence, a high efficiency of H₂ evolution was achieved for TiO₂-SDA with 0.95 mmol h^-1 g^-1 (AQE ∼45.6 % at 365 nm) under solar light irradiation without a co-catalyst. The amination modification broadens the light absorption range of the photocatalyst, inhibits the binding of photogenerated carriers, and improves the photocatalytic efficiency; which was verified by photochemical properties and DFT theoretical calculations. This covalent modification method ensures the stability of the photocatalytic reaction. This work provides an approach for molecularly modified photocatalysts to improve photocatalytic performance by covalently modifying small molecules containing amine groups on the photocatalyst surface.

Acute and chronic toxicity of amine-functionalized SiO2 nanostructures toward Daphnia magna

Silicon oxide (SiO₂) nanostructures (SiO₂NS) are increasingly being incorporated into an array of products, notably in the food, pharmaceutical, medical industries and in water treatment systems. Amorphous SiO₂NS have low toxicity, however, due to their great versatility, superficial modifications can be made and these altered structures require toxicological investigation. In this study, SiO₂NS were synthetized and amine-functionalized with the molecules (3-aminopropyl)triethoxysilane (APTMS) and 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (AEAEAPTMS), named SiO₂NS@1 and SiO₂NS@3, respectively. The bare SiO₂NS, SiO₂NS@1 and SiO₂NS@3 samples were characterized and the influence of the culture medium used in the toxicological assays was also evaluated. The effect of amine functionalization of SiO₂NS was investigated through acute and chronic toxicity assays with Daphnia magna. Modifications to ultrastructures of the intestine and eggs of these organisms were observed in TEM and SEM analysis. The toxicity was influenced by the surface modifications and a possible Trojan horse effect was highlighted, particularly in the case of chronic exposure. Exposure to all NSs promoted alterations in the microvilli and mitochondria of the D. magna intestine and some damage to egg cells was also observed. The results demonstrate the importance of carrying out a full characterization of these materials, since surface modifications can enhance their toxic potential.

NH2-CuO-MCM-41 covalently cross-linked multipurpose membrane for applications in water treatment: Removal of hazardous pollutants from water, water desalination and anti-biofouling performance

The current study was planned to fabricate a new set of membranes to target multiple application areas such as desalting, removal of micropollutants and antibiofouling performance. In-situ incorporated copper oxide to MCM-41 (CuO-MCM-41) was synthesized and amine (-NH₂) functionalized by reacting with N1-(3-trimethoxy silylpropyl) diethylenetriamine (NTSDETA) yielding NH₂-CuO-MCM-41. Different concentrations of NH₂-CuO-MCM-41 were covalently cross-linked in polyamide active layer during interfacial polymerization (IP) between N, N'-bis(3-aminopropyl)ethylenediamine and terephthaloyl chloride (TPC) on polysulfone/poly ester terephthalate (PS/PET) support. The membranes were extensively characterized by Water Contact Angle (WCA), Scanning Electron Microscopy (SEM), Fourier Transform Infra-red (FTIR) spectroscopy, Energy Dispersive X-ray (EDX) analysis, Elemental mapping and Powder X-ray Diffraction (PXRD). From among the different versions of X-CuO-MCM-41/PA@PS/PET membranes, the 0.05%-CuO-MCM-41/PA@PS/PET membrane showed best performance in terms of rejecting a variety of salts, micropollutants and antibiofouling. The 0.05%-CuO-MCM-41/PA@PS/PET showed >98% rejection of MgCl₂ and 78% rejection of caffeine with a permeate flux of 16 LMH at 25 bar. The 0.1-NH₂-CuO-MCM-41inhibited S. aureus growth by 51.7%. Hence, the current strategy of membrane fabrication proved to be highly efficient for multipurpose applications in water treatment.

Adsorption of CO2 by a novel zeolite doped amine modified ternary aerogels

Novel amine functionalized materials can capture greenhouse gas CO₂. In this study, SiO₂-Al₂O₃-ZrO₂ ternary composite aerogel was prepared by sol-gel method, supercritical drying, ultrasonic non-in-situ synthesis and other processes using aluminum chloride hexahydrate as aluminum source, ethyl orthosilicate as silicon source and tetrabbutyl zirconate as zirconium source. The composite material was used as the carrier material. By impregnation method, the modified agent bis - (3-trimethoxy-silpropyl) amine and the composite were fully mixed and modified, and the novel zeolite doped amine functionalized ternary composite aerogel was obtained by doping acidification activation zeolite. The results show that the prepared novel zeolite amine-modified ternary aerogels have rich microporous structure and ordered mesoporous structure. After loading different contents of amine-based materials (CAA-X) in the ternary aerogels, the comparison between CAAZ-X and zeolite amine-modified ternary aerogels is conducted. Zeolite doped CAAZ-30 material shows the best adsorption performance, with a maximum adsorption capacity of 5.30 mmol/g. In the presence of water vapor, CAAZ-30 material also showed the best adsorption performance, with a maximum adsorption capacity of 5.33 mmol/g. This can help us design suitable adsorbent materials for CO₂ capture in different practical applications.

Amine-Functionalized Silver Nanoparticles: A Potential Antiviral-Coating Material with Trap and Kill Efficiency to Combat Viral Dissemination (COVID-19)

The outbreak of COVID-19 has drastically affected the daily lifestyles of people globally where specific Coronavirus-2 transmits primarily by respiratory droplets. Structurally, the SARS-CoV-2 virus is made up of four types of proteins in which S-protein is indispensable among them, as it causes rapid replication in the host body. Therefore, the glycine and alanine composed of HR1 of S-protein is the ideal target for antiviral action. Different forms of surface-active PPEs can efficiently prevent this transmission in this circumstance. However, the virus can survive on the conventional PPEs for a long time. Hence, the nanotechnological approaches based on engineered nanomaterials coating on medical equipments can potentially prevent the dissemination of infections in public. Silver nanoparticles with tuneable physicochemical properties and versatile chemical functionalization provide an excellent platform to combat the disease. The coating of amine-functionalized silver nanoparticle (especially amine linked to aliphatic chain and trialkoxysilane) in its nanostructured form enables cloths trap and kill efficient. PPEs are a primary and reliable preventive measure, although they are not 100% effective against viral infections. So, developing and commercializing surface-active PPEs with trap and kill efficacy is highly needed to cope with current and future viral infections. This review article discusses the COVID-19 morphology, antiviral mechanism of Ag-NPs against SARS-CoV-2 virus, surface factors that influence viral persistence on fomites, the necessity of antiviral PPEs, and the potential application of amine-functionalized silver nanoparticles as a coating material for the development of trap and kill-efficient face masks and PPE kits.

New porous amine-functionalized biochar-based desiccated coconut waste as efficient CO2 adsorbents

Climate change caused by the greenhouse gases CO2 remains a topic of global concern. To mitigate the excessive levels of anthrophonic CO2 in the atmosphere, CO2 capture methods have been developed and among these, adsorption is an especially promising method. This paper presents a series of amine functionalized biochar obtained from desiccated coconut waste (amine-biochar@DCW) for use as CO2 adsorbent. They are ethylenediamine-functionalized biochar@DCW (EDA-biochar@DCW), diethylenetriamine-functionalized biochar@DCW (DETA-biochar@DCW), triethylenetetramine-functionalized biochar@DCW (TETA-biochar@DCW), tetraethylenepentamine-functionalized biochar@DCW (TEPA-biochar@DCW), and pentaethylenehexamine-functionalized biochar@DCW (PEHA-biochar@DCW). The adsorbents were obtained through amine functionalization of biochar and they are characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, Brunauer-Emmett-Teller (BET), and thermogravimetric analysis (TGA). The CO2 adsorption study was conducted isothermally and using a thermogravimetric analyzer. From the results of the characterization analyses, a series of amine-biochar@DCW adsorbents had larger specific surface area in the range of 16.2 m2/g-37.1 m2/g as compare to surface area of pristine DCW (1.34 m2/g). Furthermore, the results showed an increase in C and N contents as well as the appearance of NH stretching, NH bending, CN stretching, and CN bending, suggesting the presence of amine on the surface of biochar@DCW. The CO2 adsorption experiment shows that among the amine modified biochar adsorbents, TETA-biochar@DCW has the highest CO2 adsorption capacity (61.78 mg/g) when using a mass ratio (m:m) of biochar@DCW:TETA (1:2). The adsorption kinetics on the TETA-biochar@DCW was best fitted by the pseudo-second model (R2 = 0.9998), suggesting the adsorption process occurs through chemisorption. Additionally, TETA-biochar@DCW was found to have high selectivity toward CO2 gas and good reusability even after five CO2 adsorption-desorption cycles. The results demonstrate the potential of novel CO2 adsorbents based on amine functionalized on desiccated coconut waste biochar.

Surface modifications of biopolymers for removal of per- and polyfluoroalkyl substances from water: Current research and perspectives

Per- and polyfluoroalkyl substances (PFAS) are highly recalcitrant organic contaminants that have attracted ever-increasing attention from the general public, government agencies and scientific communities. To remove PFAS from water, especially the enormous volume of drinking water, stormwater, and groundwater, sorption is the most practical approach. Success of this approach demands green, renewable, and sustainable materials for capturing PFAS at ng/L or µg/L levels. To meet this demand, this manuscript critically reviewed sorbents developed from biopolymers, such as chitosan (CTN), alginate (ALG), and cellulose (CEL) covering the period from 2008 to 2023. The use of different cross-linkers for the surface modifications of biopolymers were described. The underlying removal mechanism of biosorbents for PFAS adsorption from molecular perspectives was discussed. Besides reviewing and comparing the performance of different bio-based sorbents with respect to environmental factors like pH, and sorption kinetics and capacity, strategies for modifying biosorbents for better performance were proposed. Additionally, approaches for regeneration and reuse of the biosorbents were discussed. This was followed by further discussion of challenges facing the development of biosorbents for PFAS removal.

A novel amine functionalized porous geopolymer spheres from municipal solid waste incineration fly ash for CO2 capture

Municipal solid waste (MSW) incineration fly ash (FA) is classified as hazardous waste, and strategies for recycling FA have attracted attention. In this study, the porous geopolymer spheres (PGS) were prepared from FA by the foaming-suspension-solidification method, and then the PGS were functionalized with tetraethylenepentamine (TEPA) to capture CO2. The results showed that washing pretreatment and the addition of H2O2 foaming agent enhanced the pore volume and specific surface area of PGS. The CO2 adsorption capacity of amine-functionalized PGS exhibited a trend of increasing and then decreasing in the range of 35-80 °C. The maximum adsorption capacity of TEPA-WPGS3 was 2.55 mmol/g at 65 °C higher than expected for the average of TEPA and PGS. This was because PGS improved the dispersion of TEPA, thus exposing more active sites of TEPA and making it more likely to interact with CO2. The adsorption efficiency of amine-functionalized PGS decreased by only 2.4% after 10 cycles, indicating that it has excellent regeneration performance. In addition, amine-functionalized PGS, which showed excellent CO2 adsorption capacity, had a significant ability to selectively adsorb CO2 and the adsorption capacity of the rapid stage accounted for approximately 80% of the saturated adsorption capacity. This study shows that FA-derived geopolymers have excellent CO2 adsorption properties and provides a new method for the resource utilization of FA.

Design and development of biomimetic electrospun sulphonated polyether ether ketone nanofibrous scaffold for bone tissue regeneration applications: in vitro and in vivo study

Bone defect restoration remains challenging in orthopedic medical practices. In this study an attempt is carried out to probe the use of new biomimetic SPEEK (sulfonated polyether ether ketone) based nanofibrous scaffold to deliver amine functionalized hydroxyapatite nanoparticles loaded resveratrol for its potent functionality in osteogenic differentiation. SPEEK polymer with reactive functional group SO₃H was synthesized through process of sulphonation reaction. Amine functionalized nanoparticles with protonated amino groups revamp the molecular interaction by the formation of hydrogen bonds that in turn intensify the bioactivity of the nanofibrous scaffold. Osteoconductive functionalized nanohydroxyapatite enhances the cell proliferation and osteogenicity with improved cell attachment and spreading. The results of FT-IR, XRD, Carbon-Silica NMR and EDX analysis confirmed the amine functionalization of the hydroxyapatite nanoparticles. Surface morphological analysis of the fabricated nanofibers through SEM and AFM analysis shows vastly interconnected porous structure that mimics the bone extracellular matrix, which enhances the cell compatibility. Cell adhesion and live dead assay of the nanoscaffolds express less cytotoxicity. Mineralization and alkaline phosphatase assay establish the osteogenic differentiation of the nanofibrous scaffold. The in vitro biocompatibility studies reveal that the fabricated scaffold was osteo-compatible with MG63 cell lines. Hemocompatibility study further proved that the designed biomimetic nanofibrous scaffold was highly suitable for bone tissue engineering. The results of in vivo analysis in zebrafish model for the fabricated nanofibers demonstrated significant increase in the caudal fin regeneration indicating mineralization of osteoblast. Thus, the commending results obtained instigate the potentiality of the composite nanofibrous scaffold as an effective biomimetic substrate for bone tissue regeneration.