A Co-Crystallised Cobalt(II) Cluster of Pyridinedicarboxylic Acid (PDC) as a Luminescent Material for Selective Sensing of Methanol.

A luminescent Cobalt(II) co-crystal [Co13(PDC)16(H2O)24.7H2O] 1 (where H2PDC = 2,6-pyridinedicarboxylic acid) have been prepared by oven-heating and slow evaporation of solvent. Single crystal X-ray diffraction (SCXRD) analysis revealed that 1 is a mixture of complexes that crystallizes in the triclinic space group P-1 and the geometry around the Co(II) ions is octahedral. The structure is extensively imbued with hydrogen bonding that helps in stabilizing the complex. Thermogravimetric analysis indicates that 1 is thermally stable up to 364 οC. The luminescence properties of 1 revealed a strong emission centered at 437 nm (λex = 345 nm) assigned to ligand to metal charge transfer (LMCT). The luminescence sensing of 1 towards volatile organic molecules were also examined. However, 1 displayed a turn off towards methanol compared to other molecules with high quenching efficiency and low limit of detection (3.5 × 10-4 vol%). The results show excellent selectively and high sensitivity. Powder X-ray diffraction studies revealed that the structural integrity of the complex was maintained after exposure to methanol vapour. Theoretical studies also revealed small binding energy (-413.2 au) and low energy gap (1.19) for 1-CH3OH adduct.

Capacity building in porous materials research for sustainable energy applications.

The project aimed to develop porous materials for sustainable energy applications, namely, hydrogen storage, and valorization of biomass to renewable fuels. At the core of the project was a training programme for Africa-based researchers in (i) the exploitation of renewable locally available raw materials; (ii) the use of advanced state-of-the-art techniques for the design and synthesis of porous materials (zeolites and metal-organic frameworks (MOFs)) for energy storage; and (iii) the valorization of sustainable low-value feedstock to renewable fuels. We found that compaction of the UiO-66 MOF at high pressure improves volumetric hydrogen storage capacity without any loss in gravimetric uptake, and experimentally demonstrated the temperature-dependent dynamic behaviour of UiO-66, which allowed us to propose an activation temperature of ≤ 150°C for UiO-66. Co-pelletization was used to fabricate UiO-66/nanofibre monoliths as hierarchical porous materials with enhanced usable (i.e. deliverable) hydrogen storage capacity. We clarified the use of naturally occurring kaolin as a source of silica and alumina species for zeolite synthesis. The kaolin-derived zeolite X was successfully used as a catalyst for the transesterification of Jatropha curcas oil (from non-edible biomass) to biodiesel. We also prepared porous composites (i.e. carbon/UiO-66, organoclay/UiO-66 and zeolite/carbon) that were successfully applied in electrochemical sensing.

Synthesis and Characterization of Doped Magnesium Hydroxide for Medium Heat Storage Application.

The amount of waste heat generated annually in the UK exceeds the total annual electricity demand. Hence, it is crucial to effectively harness all available sources of waste heat based on their varying temperatures. Through suitable technologies, a substantial portion of this waste heat has the potential to be recovered for reutilization. Thermochemical energy storage (TCES) provides the best opportunities to recover waste heat at various temperatures for long-term storage and application. The potential of TCES with magnesium hydroxide, Mg(OH)2, has been established, but it has a relatively high dehydration temperature, thus limiting its potential for medium-temperature heat storage applications, which account for a vast proportion of industrial waste heat. To this end, samples of doped Mg(OH)2 with varying proportions (5, 10, 15, and 20 wt%) of potassium nitrate (KNO3) have been developed and characterized for evaluation. The results showed that the Mg(OH)2 sample with 5 wt% KNO3 achieved the best outcome and was able to lower the dehydration temperature of the pure Mg(OH)2 from about 317 °C to 293 °C with an increase in the energy storage capacity from 1246 J/g to 1317 J/g. It also showed a monodisperse surface topology and thermal stability in the non-isothermal test conducted on the sample and therefore appears to have the potential for medium heat storage applications ranging from 293 °C to 400 °C.

Solvothermal synthesis of organoclay/Cu-MOF composite and its application in film modified GCE for simultaneous electrochemical detection of deoxyepinephrine, acetaminophen and tyrosine.

An organoclay/copper-based metal-organic framework (MOF) composite was synthesized using a solvothermal method by growing a Cu-BTC (copper(ii) benzene-1,3,5-tricarboxylate) MOF from a mixture of the MOF precursor solution in which various amounts of organoclay had been dispersed. The organoclay was obtained by intercalating a cationic dye, namely thionin, into a natural Cameroonian clay sampled in Sagba deposit (North West of Cameroon). The organoclay and the as-synthesized composites were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and Brunauer, Emmett and Teller (BET) techniques. From Scherrer's equation, the crystallite size of the composite was found to be between 55 and 58 nm, twice as large as the pristine MOF's crystallite size. The organoclay/Cu-MOF composite (Sa-TN50/Cu3(BTC)2) exhibiting a BET surface area of 192 m2 g-1, about twice that of pristine clay and about one seventh that of pristine MOF, was then utilized to form a stable thin film onto glassy carbon electrodes (GCE) by drop coating (Sa-TN50/Cu3(BTC)2/GCE). These electrodes demonstrated electrocatalytic behavior toward deoxyepinephrine (DXEP) and thus enabled selective and simultaneous sensitive detection of three analytes: DXEP, acetaminophen (AC) and tyrosine (TYR) compared with bare GCE and clay modified electrode. Under optimum conditions, Sa-TN50/Cu3(BTC)2/GCE exhibited good performance including large calibration curves ranging from 5.0 µM to 138.0 µM for DXEP, 4.0 µM to 153.0 µM for AC and 1.0 µM to 29.4 µM for TYR. The detection limits were found to be, 0.4 µM, 0.7 µM and 0.2 µM for DXEP, AC and TYR, respectively. The developed sensors have been applied successfully in the quantification of AC in a commercial tablet of AC, and DXEP, AC and TYR in tap water.

Rational synthesis of microporous carbons for enhanced post-combustion CO2 capture via non-hydroxide activation of air carbonised biomass.

This work explores the use of a less corrosive activating agent, potassium oxalate (PO), in combination with difficult to activate carbonaceous matter for the preparation of activated carbons. The design of the study allowed a fuller understanding of the workings of PO compared to hydroxide (KOH) activation, and also optimised the preparation of highly microporous carbons with exceptional CO2 storage capacity under low pressure (≤1 bar) conditions at ambient temperature. The PO activated carbons have a surface area of up to 1760 m2 g-1 and are highly microporous with virtually all of the surface area arising from micropores. The porosity of the PO activated carbons can be readily tailored towards having pores of size 6-8 Å, which are highly suited for CO2 storage at low pressure (i.e., post-combustion capture). At 25 °C, the PO activated carbons can store up to 1.8 and 5.0 mmol g-1 of CO2 at 0.15 bar and 1 bar, respectively. On the other hand, KOH activated carbons reach a higher surface area of up to 2700 m2 g-1, and store up to 1.0 and 4.0 mmol g-1 of CO2. This work demonstrates that PO may be used as a mild, less corrosive and less toxic activating agent for the rational and targeted synthesis of biomass-derived activated carbons with tailored porosity. The targeted synthesis may be aided by careful selection of the biomass starting material as guided by the O/C ratio of the biomass.

Optimization of biodiesel synthesis from Jatropha curcas oil using kaolin derived zeolite Na-X as a catalyst.

Biodiesel is an alternative renewable green fuel obtainable from the reaction of plant or animal oil with a low molecular weight alcohol in the presence of a catalyst. However, the cost of its production remains high due to costly feedstock, the majority of which is competitively also used as food, and the use of homogeneous catalysts, which pose difficulties in product purification and resulting environmental pollution. The aim of this study was to explore the production of biodiesel through transesterification of non-edible and cheap Jatropha curcas (JC) oil using a zeolite Na-X catalyst obtained from naturally occurring kaolin clay. The transesterification parameters, namely reaction temperature, reaction time, catalyst loading and methanol to oil molar ratio were optimized using the L16(44) Taguchi orthogonal array approach. The catalyst loading was found to be the most influential parameter at 93.79%. The optimum conditions for the conversion of JC oil, with a biodiesel yield of up to 93.94%, were found to be a methanol to oil molar ratio of 10 : 1, catalyst loading of 8%, reaction temperature of 70 °C and reaction time of 5 h. Fuel characterization parameters were within the European Norm (EN) 14214:2019 biodiesel specifications. Our findings offer insights into the ideal parametric conditions for the cost-effective synthesis of biodiesel from JC oil via zeolite-catalyzed esterification.

Experimental Demonstration of Dynamic Temperature-Dependent Behavior of UiO-66 Metal-Organic Framework: Compaction of Hydroxylated and Dehydroxylated Forms of UiO-66 for High-Pressure Hydrogen Storage.

High-pressure (700 MPa or ∼100 000 psi) compaction of dehydroxylated and hydroxylated UiO-66 for H2 storage applications is reported. The dehydroxylation reaction was found to occur between 150 and 300 °C. The H2 uptake capacity of powdered hydroxylated UiO-66 reaches 4.6 wt % at 77 K and 100 bar, which is 21% higher than that of dehydroxylated UiO-66 (3.8 wt %). On compaction, the H2 uptake capacity of dehydroxylated UiO-66 pellets reduces by 66% from 3.8 to 1.3 wt %, while for hydroxylated UiO-66 the pellets show only a 9% reduction in capacity from 4.6 to 4.2 wt %. This implies that the H2 uptake capacity of compacted hydroxylated UiO-66 is at least three times higher than that of dehydroxylated UiO-66, and therefore, hydroxylated UiO-66 is more promising for hydrogen storage applications. The H2 uptake capacity is closely related to compaction-induced changes in the porosity of UiO-66. The effect of compaction is greatest in partially dehydroxylated UiO-66 samples that are thermally treated at 200 and 290 °C. These compacted samples exhibit XRD patterns indicative of an amorphous material, low porosity (surface area reduces from between 700 and 1300 m2/g to ca. 200 m2/g and pore volume from between 0.4 and 0.6 cm3/g to 0.1 and 0.15 cm3/g), and very low hydrogen uptake (0.7-0.9 wt % at 77 K and 100 bar). The observed activation-temperature-induced dynamic behavior of UiO-66 is unusual for metal-organic frameworks (MOFs) and has previously only been reported in computational studies. After compaction at 700 MPa, the structural properties and H2 uptake of hydroxylated UiO-66 remain relatively unchanged but are extremely compromised upon compaction of dehydroxylated UiO-66. Therefore, UiO-66 responds in a dynamic manner to changes in activation temperature within the range in which it has hitherto been considered stable.

Hydrogen storage in high surface area carbons: experimental demonstration of the effects of nitrogen doping.

The influence of nitrogen doping on the hydrogen uptake and storage capacity of high surface area carbon materials is presented in this report. To generate suitable study materials, we have exploited the relationship between synthesis conditions and textural properties of zeolite-templated carbons to generate a range of high surface area carbons with similar pore size distribution but which are either N-doped or N-free. For N-doped carbons, the nitrogen content was kept within a narrow range of between 4.7 and 7.7 wt %. The carbon materials, irrespective of whether they were doped or not, exhibited high surface area (1900-3700 m(2)/g) and pore volume (0.99 and 1.88 cm(3)/g), a micropore surface area of 1500-2800 m(2)/g, and a micropore volume of 0.65-1.24 cm(3)/g. The hydrogen uptake varied between 4.1 and 6.9 wt %. We present experimental data that indicates that the effect of N-doping on hydrogen uptake is only apparent when related to the surface area and pore volume associated with micropores rather than total porosity. Furthermore, by considering the isosteric heat of hydrogen adsorption and excess hydrogen uptake on N-free or N-doped carbons, it is shown that N-doping can be beneficial at lower coverage (low hydrogen uptake) but is detrimental at higher coverage (higher hydrogen uptake). The findings are consistent with previous theoretical predictions on the effect of N-doping of carbon on hydrogen uptake. The findings, therefore, add new insights that are useful for the development of carbon materials with enhanced hydrogen storage capacity.

Pore Characteristics for Efficient CO2 Storage in Hydrated Carbons.

Development of new approaches for carbon dioxide (CO2) capture is important in both scientific and technological aspects. One of the emerging methods in CO2 capture research is based on the use of gas-hydrate crystallization in confined porous media. Pore dimensions and surface functionality of the pores play important roles in the efficiency of CO2 capture. In this report, we summarize work on several porous carbons (PCs) that differ in pore dimensions that range from supermicropores to mesopores, as well as surfaces ranging from hydrophilic to hydrophobic. Water was imbibed into the PCs, and the CO2 uptake performance, in dry and hydrated forms, was determined at pressures of up to 54 bar to reveal the influence of pore characteristics on the efficiency of CO2 capture and storage. The final hydrated carbon materials had H2O-to-carbon weight ratios of 1.5:1. Upon CO2 capture, the H2O/CO2 molar ratio was found to be as low as 1.8, which indicates a far greater CO2 capture capacity in hydrated PCs than ordinarily seen in CO2-hydrate formations, wherein the H2O/CO2 ratio is 5.72. Our mechanistic proposal for attainment of such a low H2O/CO2 ratio within the PCs is based on the finding that most of the CO2 is captured in gaseous form within micropores of diameter <2 nm, wherein it is blocked by external CO2-hydrate formations generated in the larger mesopores. Therefore, to have efficient high-pressure CO2 capture by this mechanism, it is necessary to have PCs with a wide pore size distribution consisting of both micropores and mesopores. Furthermore, we found that hydrated microporous or supermicroporous PCs do not show any hysteretic CO2 uptake behavior, which indicates that CO2 hydrates cannot be formed within micropores of diameter 1-2 nm. Alternatively, mesoporous and macroporous carbons can accommodate higher yields of CO2 hydrates, which potentially limits the CO2 uptake capacity in those larger pores to a H2O/CO2 ratio of 5.72. We found that high nitrogen content prevents the formation of CO2 hydrates presumably due to their destabilization and associated increase in system entropy via stronger noncovalent interactions between the nitrogen functional groups and H2O or CO2.

Optimization of the Pore Structure of Biomass-Based Carbons in Relation to Their Use for CO2 Capture under Low- and High-Pressure Regimes.

A versatile chemical activation approach for the fabrication of sustainable porous carbons with a pore network tunable from micro- to hierarchical micro-/mesoporous is hereby presented. It is based on the use of a less corrosive and less toxic chemical, i.e., potassium oxalate, rather than the widely used KOH. The fabrication procedure is exemplified for glucose as precursor, although it can be extended to other biomass derivatives (saccharides) with similar results. When potassium oxalate alone is used as activating agent, highly microporous carbons are obtained (SBET ≈ 1300-1700 m2 g-1). When a melamine-mediated activation process is used, hierarchical micro-/mesoporous carbons with surface areas as large as 3500 m2 g-1 are obtained. The microporous carbons are excellent adsorbents for CO2 capture at low pressure and room temperature, able to adsorb 4.2-4.5 mmol CO2 g-1 at 1 bar and 1.1-1.4 mmol CO2 g-1 at 0.15 bar. However, the micro-/mesoporous carbons provide record-high room temperature CO2 uptakes at 30 bar of 32-33 mmol g-1 CO2 and 44-49 mmol g-1 CO2 at 50 bar. The findings demonstrate the key relevance of pore size in CO2 capture, with narrow micropores having the leading role at pressures <1 bar and supermicropores/small mesopores at high pressures. In this regard, the fabrication strategy presented here allows fine-tuning of the pore network to maximize both the overall CO2 uptake and the working capacity at any target pressure.

Novel one step hydrothermal synthesis of TiO2/WO3 nanocomposites with enhanced photocatalytic activity.

A novel and simple one step hydrothermal process is used to prepare TiO(2)/WO(3) nanocomposites, in which WO(3) and TiO(2) are present in hexagonal and anatase crystalline forms, respectively, and have enhanced photocatalytic activity towards trichloroethylene degradation in the gas phase.

Oxygen-rich microporous carbons with exceptional hydrogen storage capacity.

Porous carbons have been extensively investigated for hydrogen storage but, to date, appear to have an upper limit to their storage capacity. Here, in an effort to circumvent this upper limit, we explore the potential of oxygen-rich activated carbons. We describe cellulose acetate-derived carbons that combine high surface area (3800 m2 g-1) and pore volume (1.8 cm3 g-1) that arise almost entirely (>90%) from micropores, with an oxygen-rich nature. The carbons exhibit enhanced gravimetric hydrogen uptake (8.1 wt% total and 7.0 wt% excess) at -196 °C and 20 bar, rising to a total uptake of 8.9 wt% at 30 bar, and exceptional volumetric uptake of 44 g l-1 at 20 bar, and 48 g l-1 at 30 bar. At room temperature they store up to 0.8 wt% (excess) and 1.2 wt% (total) hydrogen at only 30 bar, and their isosteric heat of hydrogen adsorption is above 10 kJ mol-1.

Crystalline-like molecularly ordered mesoporous aluminosilicates derived from aluminosilica-surfactant mesophases via benign template removal.

We report the preparation of mesoporous aluminosilicate materials that exhibit molecular-scale ordering in their pore wall framework. The materials were derived from mesoporous aluminosilica-surfactant mesophases via benign template removal methods, which allowed the retention of molecular ordering in surfactant-free materials. The molecularly ordered aluminosilica-surfactant mesophases were obtained from hydrothermal crystallization of cetyltrimethylammonium hydroxide/Al,Si/H2O systems at 135 degrees C for 12 days. Benign template removal via H2O2-mediated oxidation of the surfactant at room temperature was found to be the most effective method in generating surfactant-free materials with molecular ordering, high textural properties (depending on Al content), and high acidity. The Al in the resulting aluminosilicates was entirely incorporated in framework (tetrahedrally coordinated) sites. Template extraction in acidified ethanol also generated molecularly ordered materials but compromised the Al content and acidity. Template removal via conventional calcination generated porous materials with high textural properties but which exhibited only limited molecular ordering and had relatively low acidity and significant amounts of nonframework Al. This work demonstrates that molecular ordering in mesoporous silicate-surfactant mesophases is due to crystallographic ordering within inorganic frameworks rather than the arrangement/packing of surfactant molecules.

Surfactant mediated control of pore size and morphology for molecularly ordered ethylene-bridged periodic mesoporous organosilica.

A series of ethylene-containing mesoporous organosilica materials were fabricated via surfactant-mediated assembly of 1,2-bis(triethoxysilyl)ethylene (BTEE) organosilica precursor using alkyltrimethylammonium bromide (CnTAB) surfactants with different alkyl chain length (n=12, 14, 16, 18) as supramolecular templates. The presence of molecularly ordered ethylene groups in the resulting periodic mesoporous organosilica (PMO) materials was confirmed by XRD data along with 29Si and 13C MAS NMR analysis. Additional characterization techniques, namely nitrogen sorption, TEM, and TGA, confirmed the structural ordering and thermal stability of the molecularly ordered ethylene-bridged PMOs. The PMOs exhibit molecular-scale ordering (with a periodicity of 5.6 A) within the organosilica framework and tunable pore size, which depending on the alkyl chain length of the surfactant templates, varied in the range 23-41 A. Furthermore, depending on the alkyl chain length of the templates, the particle morphology of the PMOs gradually changed from monodisperse spheres (for C12TAB) to rod or cakelike particles (for C14TAB) and elongated ropelike particles for longer chain surfactants. Variations in the surfactant chain length therefore allowed control of both the pore size and particle morphology without compromising molecular-scale or structural ordering. The reactivity of ethylene groups was probed by bromination, which demonstrated the potential for further functionalization of the PMOs.

Preparation and hydrogen storage properties of zeolite-templated carbon materials nanocast via chemical vapor deposition: effect of the zeolite template and nitrogen doping.

Carbon materials have been prepared using zeolite 13X or zeolite Y as template and acetonitrile or ethylene as carbon source via chemical vapor deposition (CVD) at 550-1000 degrees C. Materials obtained from acetonitrile at 750-850 degrees C (zeolite 13X) or 750-900 degrees C (zeolite Y) have high surface area (1170-1920 m(2)/g), high pore volume (0.75-1.4 cm(3) g(-1)), and exhibit some structural ordering replicated from the zeolite templates. Templating with zeolite Y generally results in materials with higher surface area. High CVD temperature (> or =900 degrees C) results in low surface area materials that have significant proportions of graphitic carbon and no zeolite-type structural ordering. The nitrogen content of the samples derived from acetonitrile varies between 5 and 8 wt %. When ethylene is used as a carbon precursor, high surface area (800-1300 m(2)/g) materials are only obtained at lower CVD temperature (550-750 degrees C). The ethylene-derived carbons retain some zeolite-type pore channel ordering but also exhibit significant levels of graphitization even at low CVD temperature. In general, the carbon materials retain the particle morphology of the zeolite templates, with solid-core particles obtained at 750-850 degrees C while hollow shells are generated at higher CVD temperature (> or =900 degrees C). We observed hydrogen uptake of up to 4.5 wt % and 45 g H(2)/L (volumetric density) at -196 degrees C and 20 bar for the carbon materials. The hydrogen uptake was found to be dependent on surface area and was therefore influenced by the choice of zeolite template and carbon source. Zeolite Y-templated N-doped carbons had the highest hydrogen uptake capacity. Gravimetric and volumetric methods gave similar uptake capacity at 1 bar (i.e., 1.6 and 2.0 wt % for zeolite 13X and Y-templated N-doped carbons, respectively). Our findings show that zeolite-templated carbons are attractive for hydrogen storage and highlight the potential benefits of functionalization (nitrogen-doping).

Synthesis and characterization of novel mesoporous aluminosilicate MCM-41 containing aluminophosphate building units.

Novel MCM-41 aluminosilicate/aluminophosphate materials that exhibit good mesostructural ordering have been synthesized and characterised; the synthesis of these silicoaluminophosphates involved the use of gel mixtures containing amorphous mesoporous aluminosilicate and aluminophosphate phases as precursor.

Photophysical properties of [60]fullerenes and phthalocyanines embedded in ordered mesoporous silica films annealed at various temperatures.

The photophysical properties of fullerene and/or phthalocyanine dyes embedded in ordered mesoporous silica films and the influence of annealing temperature on the nature of the immobilized dye molecules has been investigated using photoluminescence (PL) and diffuse reflectance (DR) studies. The PL and DR studies show that fullerene (C60) and/or zinc phthalocyanine (ZnPc) molecules incorporated into transparent mesoporous silica films, via either sol-gel or grafting routes, exist predominantly in monomeric form. Careful choice of annealing temperature, between 25 and 225 degrees C, can further enhance monomeric dispersion. For C60-containing films, monomeric dispersion of fullerene was observed for annealing temperatures up to 175 degrees C for sol-gel derived films and 225 degrees C for grafted films. Both sol-gel and grafted ZnPc-containing films showed evidence of monodispersed phthalocyanine for annealing temperatures up to 225 degrees C. In general, annealing temperatures in the range 125-175 degrees C were found to yield optimal monodispersion of the dye molecules. When both C60 and ZnPc were incorporated into the silica films, no evidence of interaction between the dyes, i.e., charge-transfer transitions or the formation of fullerene/phthalocyanine charge-transfer complexes, was observed. This suggests that embedded fullerene and phthalocyanine molecules may be used for the preparation of solid-state optical limiters, based on reverse saturable absorption, where monomeric dispersion of the dye molecules is important.

Synthesis of siliceous hollow spheres with large mesopore wall structure by supercritical CO2-in-water interface templating.

Hollow silica spheres with large mesopore wall structures have been synthesized via CO(2)-in-water emulsion templating in the presence of PEO-PPO-PEO block copolymers under supercritical fluid conditions.