Eric Masika

A family of microporous carbons prepared via a simple metal salt carbonization route with high selectivity for exceptional gravimetric and volumetric post-combustion CO2 capture

Heating of a high carbon-containing metal salt under nitrogen generates microporous carbons with exceptional post-combustion CO2 capture ability. Depending on carbonisation temperature (600–1000 °C) and duration (0.5 to 4 h), microporous carbons with surface area and pore volume of 500–2100 m2 g−1 and 0.27–1.1 cm3 g−1, respectively, are generated. The proportion of microporosity is high; 96% of surface area and up to 92% of pore volume. The porosity is dominated by 6–7 A pores, which is advantageous for CO2 uptake; the carbons capture up to 4.8 mmol g−1 at 1 bar and 25 °C. Under post-combustion flue gas stream conditions (0.15 bar CO2), the carbons capture up to 1.7 mmol g−1 of CO2, which is the highest so far reported for porous carbons. The carbons have excellent selectivity for CO2 over N2; a selectivity factor of 43 based on CO2 and N2 initial adsorption rates, an Ideal Adsorbed Solution Theory (IAST) selectivity factor of 50 and an equilibrium CO2/N2 adsorption ratio at 1 bar of 22.5 compared to typical values of 5–11 for carbons. Moreover, the carbons show excellent CO2 uptake for low pressure swing operations; working capacity of up to 5.4 and 3.4 mmol g−1 for pressure swing adsorption (PSA) from a pure CO2 stream (6 to 1 bar) and flue gas stream (1.2 to 0.2 bar), respectively. The working capacity for vacuum swing adsorption (VSA) is even more remarkable; reaching 5.1 and 2.4 mmol g−1 under pure CO2 (1.5 to 0.05 bar) and flue gas (0.3 to 0.01 bar) conditions, respectively. The carbons also have excellent working capacity for temperature swing adsorption (TSA). The carbons are readily densified to high packing density of up to 1.12 g cm−3 with no penalties on textural properties or gravimetric CO2 uptake. The densification and high gravimetric uptake, gives exceptional volumetric CO2 capture capacity of 71, 187 and 320 g l−1 at 0.15, 1 and 5 bar, respectively, and unrivalled working capacity for PSA, VSA and TSA processes. The simple synthesis route, optimal pore size and exceptional CO2 uptake means that the carbons offer an unprecedented combination of characteristics for post-combustion CO2 capture.

Exceptional gravimetric and volumetric hydrogen storage for densified zeolite templated carbons with high mechanical stability

Zeolite templating successfully generates carbons with high surface area and pore volume of ca. 3300 m2 g−1 and 1.6 cm3 g−1, respectively. The templated carbons have an exceptional gravimetric hydrogen uptake of 7.3 wt% at 20 bar and −196 °C, and a projected maximum of ca. 9.2 wt%. These hydrogen uptake values are the highest ever recorded for carbon materials. The zeolite templated carbons have excellent mechanical stability and when compacted at a load of 10 tons (740 MPa) undergo densification to a packing density of ca. 0.72 g cm−3 but with hardly any loss in porosity (surface area and pore volume are little changed at ca. 3000 m2 g−1 and 1.4 cm3 g−1) or gravimetric hydrogen uptake capacity, which remains high at 7.0 wt% at 20 bar and a projected maximum of ca. 8.8 wt%. The effects of densification (i.e., increased packing density) coupled with hardly any loss in porosity or hydrogen uptake means that the densified zeolite templated carbons achieve an exceptional and unprecedented volumetric hydrogen uptake of 50 g l−1 at −196 °C and 20 bar, and an estimated maximum of up to 63 g l−1 at higher pressure.

High surface area metal salt templated carbon aerogels via a simple subcritical drying route: preparation and CO2 uptake properties

We describe a very simple method for the formation of high surface area carbon aerogels from melamine–formaldehyde resins, via metal salt (CaCl2) templating, wherein subcritical drying is used and no activation is required. The metal salt acts as a porogen to generate carbon aerogels with surface area of up to 1100 m2 g−1, which exhibit significant CO2 uptake of up to 2.2 mmol g−1 at 298 K and 1 bar.

Supercritical CO2 Mediated Incorporation of Pd onto Templated Carbons: A Route to Optimizing the Pd Particle Size and Hydrogen Uptake Density

Palladium nanoparticles are deposited onto zeolite template carbon (ZTC) via supercritical CO2 (scCO2) mediated hydrogenation of a CO2-phillic transition metal precursor. The supercritical fluid (SCF) mediated metal incorporation approach enabled the decoration of ZTC with 0.2-2.0 wt % of well-dispersed Pd nanoparticles of size 2-5 nm. The resulting Pd-doped ZTCs exhibit enhanced hydrogen uptake and storage density. The ZTC (with surface area of 2046 m(2)/g) had a hydrogen storage capacity (at 77 K and 20 bar) of 4.9 wt %, while the Pd-ZTCs had uptake of 4.7-5.3 wt % despite a surface area in the range 1390-1858 m(2)/g. The Pd-ZTCs thus exhibit enhanced hydrogen storage density (14.3-18.3 μmol H2/m(2)), which is much higher than that of Pd-free ZTC (12.0 μmol H2/m(2)). The hydrogen isosteric heat of adsorption (Qst) was found to be higher for the Pd-doped carbons (6.7 kJ/mol) compared to the parent ZTC (5.3 kJ/mol). The deposition of small amounts of Pd (up to 2 wt %) along with well-dispersed Pd nanoparticles of size of 2-5 nm is essential for the enhancement of hydrogen uptake and illustrates the importance of optimizing the balance between metal loading/particle size and surface area to achieve the best metal/porous carbon composite for enhanced hydrogen uptake.

Green Synthesis and Characterization of Silver Nanoparticles Using Citrullus lanatus Fruit Rind Extract

The wide-scale application of silver nanoparticles (AgNPs) in areas such as chemical sensing, nanomedicine, and electronics has led to their increased demand. Current methods of AgNPs synthesis involve the use of hazardous reagents and toxic solvents. There is a need for the development of new methods of synthesizing AgNPs that use environmentally safe reagents and solvents. This work reports a green method where silver nanoparticles (AgNPs) were synthesized using silver nitrate and the aqueous extract of Citrullus lanatus fruit rind as the reductant and the capping agent. The optimized conditions for the AgNPs synthesis were a temperature of 80°C, pH 10, 0.001 M AgNO3, 250 g/L watermelon rind extract (WMRE), and a reactant ratio of 4 : 5 (AgNO3 to WMRE). The AgNPs were characterized by Ultraviolet-Visible (UV-Vis) spectroscopy exhibiting a λmax at 404 nm which was consistent with the spectra of spherical AgNPs within the wavelength range of 380–450 nm, and Cyclic Voltammetry (CV) results showed a distinct oxidation peak at +291 mV while the standard reference AgNPs (20 nm diameter) oxidation peak occurred at +290 mV, and Transmission Electron Microscopy (TEM) revealed spherical shaped AgNPs. The AgNPs were found to have an average diameter of 17.96 ± 0.16 nm.

Antimicrobial Photodynamic Activity of Phthalocyanine Derivatives

Microbial pathogens have increasingly shown multidrug resistance posing a serious threat to the public health. Advances in technology are opening novel avenues for discovery of compounds that will mitigate the ever-increasing drug-resistant microbes. Use of photodynamic photosensitizer is one of the promising alternative approaches since they offer low risk of bacteria resistance as they use generated reactive oxygen species to kill the microbes. Phthalocyanine (Pc) is one such photosensitizer which has already shown promising antimicrobial photodynamic therapeutic properties. Previous studies have shown effectiveness of the Pc against Gram-positive bacteria. However, its effectiveness toward Gram-negative bacteria is limited by the impermeability of the bacteria’s outer membrane which is made up of lipopolysaccharides layer. The effectiveness of this photosensitizer is determined by its photophysical and photochemical properties such as singlet/triplet lifetimes, singlet oxygen quantum yields, and fluorescence quantum yield. Therefore, this review focuses on the recent significance advances on designing Pc that have this improved property by either conjugating with nanoparticles, quantum dots, functional groups in peripheral position, considering effect of cationic charge, and its position on the macrocycle.