Carbon Capture Using Porous Silica Materials.

As the primary greenhouse gas, CO2 emission has noticeably increased over the past decades resulting in global warming and climate change. Surprisingly, anthropogenic activities have increased atmospheric CO2 by 50% in less than 200 years, causing more frequent and severe rainfall, snowstorms, flash floods, droughts, heat waves, and rising sea levels in recent times. Hence, reducing the excess CO2 in the atmosphere is imperative to keep the global average temperature rise below 2 °C. Among many CO2 mitigation approaches, CO2 capture using porous materials is considered one of the most promising technologies. Porous solid materials such as carbons, silica, zeolites, hollow fibers, and alumina have been widely investigated in CO2 capture technologies. Interestingly, porous silica-based materials have recently emerged as excellent candidates for CO2 capture technologies due to their unique properties, including high surface area, pore volume, easy surface functionalization, excellent thermal, and mechanical stability, and low cost. Therefore, this review comprehensively covers major CO2 capture processes and their pros and cons, selecting a suitable sorbent, use of liquid amines, and highlights the recent progress of various porous silica materials, including amine-functionalized silica, their reaction mechanisms and synthesis processes. Moreover, CO2 adsorption capacities, gas selectivity, reusability, current challenges, and future directions of porous silica materials have also been discussed.

Recent advances in biopolymer-based advanced oxidation processes for dye removal applications: A review.

Over the past few years, synthetic dye-contaminated wastewater has attracted considerable global attention due to the low biodegradability and the ability of organic dyes to persist and remain toxic, causing numerous health and environmental concerns. As a result of the recalcitrant nature of those complex organic dyes, the remediation of wastewater using conventional wastewater treatment techniques is becoming increasingly challenging. In recent years, advanced oxidation processes (AOPs) have emerged as a potential alternative to treat organic dyestuffs discharged from industries. The most widely employed AOPs include photocatalysis, ozonation, Fenton oxidation, electrochemical oxidation, catalytic heterogeneous oxidation, and ultrasound irradiation. These processes involve the generation of highly reactive radicals to oxidize organic dyes into innocuous minerals. However, many conventional AOPs suffer from several setbacks, including the high cost, high consumption of reagents and substrates, self-agglomeration of catalysts, limited reusability, and the requirement of light, ultrasound, or electricity. Therefore, there has been significant interest in improving the performance of conventional AOPs using biopolymers and heterogeneous catalysts such as metal oxide nanoparticles (MONPs). Biopolymers have been widely considered in developing green, sustainable, eco-friendly, and low-cost AOP-based dye removal technologies. They inherit intriguing properties like biodegradability, renewability, nontoxicity, relative abundance, and sorption. In addition, the immobilization of catalysts on biopolymer supports has been proven to possess excellent catalytic activity and turnover numbers. The current review provides comprehensive coverage of different AOPs and how efficiently biopolymers, including cellulose, chitin, chitosan, alginate, gelatin, guar gum, keratin, silk fibroin, zein, albumin, lignin, and starch, have been integrated with heterogeneous AOPs in dye removal applications. This review also discusses the general degradation mechanisms of AOPs, applications of biopolymers in AOPs and the roles of biopolymers in AOPs-based dye removal processes. Furthermore, key challenges and future perspectives of biopolymer-based AOPs have also been highlighted.

Preparation and Characterization of Dual-Modified Cassava Starch-Based Biodegradable Foams for Sustainable Packaging Applications.

Starch and its derivatives have recently emerged as a sustainable and renewable alternative for petroleum-based expanded polystyrene (EPS) and expanded polypropylene (EPP) foam materials. In this study, biodegradable foam materials were prepared from cassava starch using a novel dual modification technique, combining microwave treatment and freeze-drying. The foam materials were prepared from starch solutions microwaved over different intervals. The starch-based foam materials were characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), 13C nuclear magnetic resonance (13C-NMR) spectroscopy, and compression set test. Moreover, the water absorption capacities and density values of the foam materials were measured according to ASTM standards. The biodegradability test was carried out according to the aerobic compost environment test. The lowest water absorption capacities of 65.56% and 70.83% were exhibited for the cassava starch foam sample (MWB) prepared at a 20 s microwave treatment time and immersed in distilled water for 2 and 24 h, respectively. Furthermore, the lightweight cassava starch-based foam materials displayed density ranging from 124 to 245 kg/m3. The biodegradation test exhibited significant biodegradation of over 50% after 15 days for all the foam materials prepared. These results suggest that the dual-modified cassava starch-based biodegradable foams show potential in sustainable packaging applications by replacing petroleum-based materials.

Development of Starch-Based Materials Using Current Modification Techniques and Their Applications: A Review.

Starch is one of the most common biodegradable polymers found in nature, and it is widely utilized in the food and beverage, bioplastic industry, paper industry, textile, and biofuel industries. Starch has received significant attention due to its environmental benignity, easy fabrication, relative abundance, non-toxicity, and biodegradability. However, native starch cannot be directly used due to its poor thermo-mechanical properties and higher water absorptivity. Therefore, native starch needs to be modified before its use. Major starch modification techniques include genetic, enzymatic, physical, and chemical. Among those, chemical modification techniques are widely employed in industries. This review presents comprehensive coverage of chemical starch modification techniques and genetic, enzymatic, and physical methods developed over the past few years. In addition, the current applications of chemically modified starch in the fields of packaging, adhesives, pharmaceuticals, agriculture, superabsorbent and wastewater treatment have also been discussed.

Development of Alumina⁻Mesoporous Organosilica Hybrid Materials for Carbon Dioxide Adsorption at 25 °C.

Two series of alumina (Al2O3)⁻mesoporous organosilica (Al⁻MO) hybrid materials were synthesized using the co-condensation method in the presence of Pluronic 123 triblock copolymer. The first series of Al⁻MO samples was prepared using aluminum nitrate nanahydrate (Al⁻NN) and aluminum isopropoxide (Al⁻IP) as alumina precursors, and organosilanes with three different bridging groups, namely tris[3-(trimethoxysilyl)propyl]isocyanurate, 1,4-bis(triethoxysilyl)benzene, and bis(triethoxysilyl)ethane. The second series was obtained using the aforementioned precursors in the presence of an amine-containing 3-aminopropyltriethoxysilane to introduce, also, hanging groups. The Al⁻IP-derived mesostructures in the first series showed the well-developed porosity and high specific surface area, as compared to the corresponding mesostructures prepared in the second series with 3-aminopropyltriethoxysilane. The materials obtained from Al⁻NN alumina precursor possessed enlarged mesopores in the range of 3⁻17 nm, whereas the materials synthesized from Al⁻IP alumina precursor displayed relatively low pore widths in the range of 5⁻7 nm. The Al⁻IP-derived materials showed high CO2 uptakes, due to the enhanced surface area and microporosity in comparison to those observed for the samples of the second series with AP hanging groups. The Al⁻NN- and Al⁻IP-derived samples exhibited the CO2 uptakes in the range of 0.73⁻1.72 and 1.66⁻2.64 mmol/g at 1 atm pressure whereas, at the same pressure, the Al⁻NN and Al⁻IP-derived samples with 3-aminopropyl hanging groups showed the CO2 uptakes in the range of 0.72⁻1.51 and 1.70⁻2.33 mmol/g, respectively. These data illustrate that Al⁻MO hybrid materials are potential adsorbents for large-scale CO2 capture at 25 °C.

Adsorption of Lead Ions from Aqueous Phase on Mesoporous Silica with P-Containing Pendant Groups.

Mesoporous silica materials with hydroxyphosphatoethyl pendant groups (POH-MS) were obtained by a two-step process: (1) block copolymer Pluronic P123-templated synthesis of mesoporous silica with diethylphosphatoethyl groups (DP-MS) by co-condensation of diethylphosphatoethyl triethoxysilane (DPTS) and tetraethylorthosilicate (TEOS) under acidic conditions and (2) conversion of diethylphosphatoethyl into hydroxyphosphatoethyl groups upon suitable treatment with concentrated hydrochloric acid. The DP-MS samples obtained by using up to 20% of DPTS featured hexagonally ordered mesopores, narrow pore size distribution and high specific surface area. Conversion of DP-MS to mesoporous silica with hydroxyphosphatoethyl groups (POH-MS) resulted in the enlargement of the specific surface area, total porosity, and microporosity. High affinity of hydroxyphosphatoethyl groups toward lead ions (Pb(2+)) makes the POH-MS materials attractive sorbents for lead ions, which is reflected by high lead uptake reaching 272 mg of Pb(2+) per gram of POH-MS. This study shows that the simple and effective co-condensation strategy assures high loading of P-containing groups showing high affinity toward lead ions, which is of great importance for removal of highly toxic lead ions from contaminated water.

Biocompatible D-Penicillamine Conjugated Au Nanoparticles: Targeting Intracellular Free Copper Ions for Detoxification.

High thiophillicicity of the Au-nanoparticle (Au NP) surface leads to covalent attachment of D-penicillamine molecules to Au NPs to form biocompatible D-penicillamine conjugated Au NPs. The latter are highly water-dispersible, exhibit no cytotoxicity, and can readily penetrate the cell membrane to target intracellular free copper ions for selective copper detoxification in the presence of the other divalent essential metal ions including Zn(II), Fe(II), Mn(II), Ca(II), and Mg(II), thus opening up a new avenue for improving the efficacy and pharmacokinetics of D-penicillamine, an important clinical drug currently used to treat the copper overload-related diseases and disorders.

CO2 adsorption on amine-functionalized periodic mesoporous benzenesilicas.

CO2 adsorption was investigated on amine-functionalized mesoporous silica (SBA-15) and periodic mesoporous organosilica (PMO) samples. Hexagonally (p6mm) ordered mesoporous SBA-15 and benzene-PMO (BPMO) samples were prepared in the presence of Pluronic P123 block copolymer template under acidic conditions. Three kinds of amine-containing organosilanes and polyethylenimine were used to functionalize SBA-15 and BPMO. Small-angle X-ray scattering and nitrogen adsorption isotherms showed that these samples featured ordered mesostructure, high surface area, and narrow pore size distributions. Solid-state (13)C- and (29)Si cross-polarization magic-angle spinning NMR spectra showed chemical linkage between amine-containing modifiers and the surface of mesoporous materials. The chemically linked amine-containing modifiers were found to be on both the inner and outer surfaces. N-[3-(trimethoxysilyl)propyl]ethylenediamine-modified BPMO (A2-BPMO) sample exhibited the highest CO2 uptake (i.e., ∼3.03 mmol/g measured on a volumetric adsorption analyzer) and the fastest adsorption rate (i.e., ∼13 min to attain 90% of the maximum amount) among all the samples studied. Selectivity and reproducibility measurements for the A2-BPMO sample showed quite good performance in flowing N2 gas at 40 mL/min and CO2 gas of 60 mL/min at 25 °C.

Selective ion exchange governed by the Irving-Williams series in K2Zn3[Fe(CN)6]2 nanoparticles: toward a designer prodrug for Wilson's disease.

The principle of the Irving-Williams series is applied to the design of a novel prodrug based on K2Zn3[Fe(CN)6]2 nanoparticles (ZnPB NPs) for Wilson's disease (WD), a rare but fatal genetic disorder characterized by the accumulation of excess copper in the liver and other vital organs. The predetermined ion-exchange reaction rather than chelation between ZnPB NPs and copper ions leads to high selectivity of such NPs for copper in the presence of the other endogenous metal ions. Furthermore, ZnPB NPs are highly water-dispersible and noncytotoxic and can be readily internalized by cells to target intracellular copper ions for selective copper detoxification, suggesting their potential application as a new-generation treatment for WD.

Mesoporous organosilica with amidoxime groups for CO2 sorption.

Incorporation of basic species such as amine-containing groups into porous materials is a well-established strategy for achieving high uptake of acidic molecules such as CO2. This work reports a successful use of the aforementioned strategy for the development of ordered mesoporous organosilica (OMO) with amidoxime groups for CO2 sorption. These materials were prepared by two-step process involving: (1) synthesis of OMO with cyanopropyl groups by co-condensation of (3-cyanopropyl)triethoxysilane and tetraethylorthosilicate in the presence of Pluronic P123 triblock copolymer under acidic conditions, and (2) conversion of cyanopropyl groups into amidoxime upon treatment with hydroxylamine hydrochloride under suitable conditions. The resulting series of amidoxime-containing OMO was prepared and used for CO2 sorption at low (25 °C) and elevated (60, 120 °C) temperatures. These sorbents exhibited relatively high adsorption capacity at ambient conditions (25 °C, 1 atm) and remarkable high sorption uptake (∼3 mmol/g) at 60 and 120 °C. This high CO2 uptake at elevated temperatures by amidoxime-containing OMO sorbent makes it a noticeable material for CO2 capture.