Chamila Gunathilake

Amidoxime-modified mesoporous silica for uranium adsorption under seawater conditions

Amidoxime-modified ordered mesoporous silica (AO-OMS) materials were prepared by a two-step process involving: (1) co-condensation synthesis of cyanopropyl-containing ordered mesoporous silica (CP-OMS), and (2) conversion of cyanopropyl into amidoxime groups. The aforementioned co-condensation synthesis is simple and less time consuming as compared to the post-synthesis grafting and assures high loading of organic groups. The intermediate CP-OMS exhibited ordered mesoporosity, high specific surface area, and narrow pore size distribution. Interestingly, conversion of CP-OMS to AO-OMS further improved its properties by enhancing the specific surface area and porosity and achieving high loading of amidoxime groups. High affinity of these groups towards uranium species makes the AO-OMS material an attractive sorbent for uranium recovery as evidenced by very high uranium uptake reaching 57 mg of uranium per gram of AO-OMS under seawater conditions.

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.

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.

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.

Mesoporous alumina–zirconia–organosilica composites for CO2 capture at ambient and elevated temperatures

New ternary and binary composite mesostructures consisting of alumina, zirconia and organosilica with isocyanurate bridging groups were synthesized via co-condensation of suitable precursors in the presence of a triblock copolymer, Pluronic P123. The resulting binary and ternary composite mesostructures were used for CO2 capture at low (0 °C), ambient (25 °C), and elevated (60 and 120 °C) temperatures. The CO2 adsorption capacities measured at 1 atm for alumina–organosilica mesostructures are: 1.43 mmol g−1 at 0 °C and 1 mmol g−1 at 25 °C. Much higher CO2 adsorption capacities were recorded at 1 atm for zirconia–organosilica mesostructures: 2.53 mmol g−1 at 0 °C and 1.93 mmol g−1 at 25 °C. This significant increase in the CO2 uptake for zirconia–organosilica was achieved due to the development of microporosity, which was shown to be beneficial for CO2 physisorption at low pressures. Temperature programmed desorption (TPD) was used to measure the CO2 sorption capacities for the mesostructures studied at 60 and 120 °C. The TPD studies revealed the superior sorption capacities of zirconia–organosilica mesostructures at 60 °C (3.02 mmol g−1) and 120 °C (2.76 mmol g−1). Various surface hydroxyls present in alumina and zirconia are primarily responsible for CO2 capture. These hydroxyls were shown to be essential for interactions with CO2 by forming hydrogen carbonate and bidentate carbonate complexes. The thermal stability, corrosion resistivity, and chemical stability of the mesostructures studied make them attractive sorbents for CO2 capture in the fossil fuel-based power plants, which generate large volumetric flow rates of flue gas at 1 atm with low partial pressure of CO2 in the temperature range of 100–150 °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 Wilsons 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 calcium oxide–silica and magnesium oxide–silica composites for CO2 capture at ambient and elevated temperatures

Incorporation of basic metal species (oxides) such as magnesium oxide and calcium oxide into porous materials is a logical strategy for enlarging the uptake of acidic greenhouse gases such as CO2. This work reports the development of ordered mesoporous silica (OMS) with incorporated magnesium and calcium oxides for CO2 sorption at ambient and elevated temperatures. These materials were prepared by using the sol–gel method in the presence of the triblock copolymer Pluronic P123 in acidic medium followed by evaporation-induced self-assembly (EISA). The resulting magnesium oxide (MgO)- and calcium oxide (CaO)-OMS materials were used for CO2 sorption at low (0, 15 °C), ambient (25 °C), and elevated (120 °C) temperatures. Temperature programmed desorption (TPD) was used to measure the CO2 sorption capacities for the mesostructures studied at 120 °C. These sorbents exhibited relatively high adsorption capacity (0.63–2.61 mmol g−1) under low (0, 15 °C) and ambient conditions (25 °C, 1 atm) and remarkably high sorption uptake (3.11–4.71 mmol g−1) at 120 °C. The observed high CO2 uptake by CaO–SiO2 and MgO–SiO2 composites under ambient conditions is caused by enhanced physisorption of CO2 in micropores. Amazingly high CO2 uptake at elevated temperatures by OMS sorbents with incorporated CaO and MgO is mainly due to the chemisorption of CO2. The well-developed porous structure together with high surface area, basic surface properties and high thermal and chemical stabilities of CaO–SiO2 and MgO–SiO2 composites increase their prospects for high temperature capture of CO2 from industrial emissions.

Mesoporous isocyanurate-containing organosilica–alumina composites and their thermal treatment in nitrogen for carbon dioxide sorption at elevated temperatures

Composite mesostructures consisting of organosilica with isocyanurate bridging groups and alumina have been synthesized using evaporation-induced self-assembly (EISA) in the presence of a triblock copolymer, Pluronic P123, in absolute ethanol solution. These mesostructures were prepared using aluminum isopropoxide and aluminum nitrate nonahydrate as alumina precursors and tris[3-(trimethoxysilyl)propyl]isocyanurate (ICS). The triblock copolymer was removed by extraction with 95% ethanol solution followed by additional thermal treatment of the extracted sample at 300 °C in flowing nitrogen; this process assured a complete removal of the polymeric template without degradation of the ICS bridging groups. The use of aluminum nitrate nonahydrate and a N-containing ICS precursor with a small amount of 3-aminopropyltriethoxysilane (AP) led to the hybrid materials with well-developed porosity and high specific surface area (200–450 m2 g−1). A controlled heating of these materials in nitrogen resulted in N-doped alumina–silica mesostructures showing high affinity towards CO2 at elevated temperatures. The use of inexpensive aluminum nitrate instead of aluminum alkoxides in the EISA synthesis had a significant impact on the pore structure, surface area and adsorption properties of the resulting composite materials.

Amidoxime-Functionalized Microcrystalline Cellulose- Mesoporous Silica Composites for Carbon Dioxide Sorption at Elevated Temperatures

Amidoxime-functionalized microcrystalline cellulose (MCC)–mesoporous silica composites were prepared for the first time by a two-step process. First, microcrystalline cellulose (MCC)–mesoporous silica with cyanopropyl groups (MCC-CP) was obtained by solvent evaporation-induced self-assembly of MCC, tetraethylorthosilicate, and (3-cyanopropyl)triethoxysilane in the presence of a Pluronic P123 triblock copolymer under acidic conditions. In the next step, the resulting material was treated with hydroxylamine hydrochloride to convert cyanopropyl groups into amidoxime functionalities to obtain a mesoporous MCC-AO composite. A series of MCC-CP and MCC-AO samples was examined for CO2 sorption at ambient (25 °C) and elevated (120 °C) temperatures. While the MCC-CP and MCC-AO samples showed relatively low CO2 uptake under ambient conditions, they performed very well at elevated temperatures (120 °C) reaching CO2 sorption capacities of 2.15–2.41 mmol g−1 (MCC-CP) and 2.84–3.85 mmol g−1 (MCC-AO). The CO2 sorption capacity of MCC-AO at 120 °C exceeds the values reported so far for many other sorbents, which makes this material attractive for CO2 capture in addition to its biocompatibility, biodegradability, non-toxicity, low cost, cycle stability, and good thermal and mechanical stability.

Amidoxime-functionalized nanocrystalline cellulose–mesoporous silica composites for carbon dioxide sorption at ambient and elevated temperatures

A series of nanocrystalline cellulose (NCC)–mesoporous silica composites (NCC-AO) with attached double-amidoxime groups is synthesized and examined for CO2 sorption at both ambient (25 °C) and elevated temperatures (120 °C). NCC-AO composites showed high CO2 uptakes at ambient pressure, namely, 3.30 mmol g−1 at 25 °C and 5.54 mmol g−1 at 120 °C. The CO2 sorption capacity of NCC-AO at 1 atm and 120 °C is very high and exceeds the values reported so far for other sorbents under the same conditions. NCC-AO sorbents exhibited very good recyclability and were stable after ten successive adsorption/desorption cycles with negligible losses of the sorption capacity. Due to the high sorption capacity, reusability, thermal stability, relatively low cost and simple synthesis route, the NCC-AO composites show good potential as effective sorbents and catalysts, including CO2 sorption at elevated temperatures.