Metal- and halogen-free synthesis of ordered mesoporous carbon materials

We thank the University of St Andrews for the PhD scholarship of FS.Mesoporous carbon materials are of great interest as catalyst supports. However, the presence of impurities such as the metal or halide ions which are often used to catalyse the polymerisation and condensation reactions in their preparation can be poisonous to the final catalyst product. For this reason, in this work, metal- and halogen-free mesoporous polymer and carbon materials (OMCs) were synthesised using a modified two phase method employing alternative polymerisation and condensation catalysts. The OMC materials synthesised exhibit a highly ordered two dimensional hexagonal arrangement of cylindrical mesopores, as revealed by small angle XRD, gas physisorption and TEM analysis, and have typical specific surface areas of ca. 600 m2/g, pore size of ca. 7.0 nm, and pore volume of approximately 0.60 cm3/g. Their physical evolution with increasing calcination temperature is examined as are the effects of varying synthesis parameters on the nature of the final mesostructure.PostprintPeer reviewe

Fixed-bed adsorption of the dye Chrysoidine R on ordered mesoporous carbon

Funding: The authors are grateful to the Ministry of Human Resource Development of the Government of India for financial support through the SPARC initiative (project: SPARC/2018-2019/P307/SL). One of the authors (AM) is thankful to MANIT, Bhopal for providing fellowship support.Herein, the efficiency of an ordered mesoporous carbon (OMC), synthesized through metal and halide free pathways, is evaluated to remove an anionic dye Chrysoidine R through fixed-bed adsorption. Potentially toxic azo dye, Chrysoidine R, was employed as a test and encouraging results are obtained. The bulk removal of the dye was accomplished with 99.77% column saturation and treatment of the exhausted bed of adsorbent with a suitable eluent resulted in almost 100% dye-recovery. The efficiency of the column remained almost unchanged in five adsorption/desorption cycles. The fixed-bed column studies clearly reveal that the OMC is a highly efficient and robust material for large-scale wastewater treatment applications.Publisher PDFPeer reviewe

Batch and bulk adsorptive removal of anionic dye using metal/halide-free ordered mesoporous carbon as adsorbent

The authors are grateful to the Ministry of Human Resource Development of the Government of India for financial support through the SPARC Project- SPARC/2018–2019/P307/SL. One of the authors (Asna Mariyam) is also grateful to MANIT, Bhopal for providing fellowship assistance. We thank the University of St Andrews for a PhD scholarship for FS. We acknowledge EPSRC Strategic Resources Grant (EP/R023751/1).The present report is an outcome of investigations to assess the adsorptive potential of a synthesized metal- and halide-free variant of ordered mesoporous carbon (OMC) towards an anionic azo dye, Methyl Orange. The results of preliminary studies, carried out in batch mode, helped in setting up the process variables to achieve optimum adsorption conditions. The experimental data were then fitted to Langmuir, Freundlich, Temkin, and Dubinin-Radushkevitch isotherm models. The equilibrium data fitted well to the Langmuir model at 303 K and the monolayer adsorption capacity was 0.33 mmol g−1. The adsorption kinetics were explored by fitting the data to pseudo-first-order and pseudo-second-order kinetic models. The latter described the kinetics well, as indicated by higher regression coefficients. To elucidate the mechanism of mass transfer, various well-known mathematical models were employed. The adsorption of the dye was found to involve particle diffusion. Thermodynamic studies revealed that the adsorptive uptake of Methyl Orange by the OMC was spontaneous (ΔG0 = −23.71 kJ mol−1) and exergonic (ΔH0 = −123.15 kJ mol−1). Finally, the bulk removal of the anionic dye was investigated through column operations followed by column regeneration (desorption) studies. Column saturation of up to 96.55% could be realized. Values for dye recovery reached up to 93.26%. The column efficiency was then evaluated by carrying out three consecutive adsorption/desorption cycles. The results obtained indicated that the adsorbent has a good ability to eliminate Methyl Orange from wastewater, both in batch and column operations.PostprintPeer reviewe

Preparation, characterisation and application of ordered mesoporous materials

The history of ordered mesoporous materials starts with the discovery of MCM-41(Mobil Composition of Matter-41) in 1992 using an organic template as structure directing agent. Mesoporous materials have not only proved to be ideal candidates in various fields like, for example, catalysis but could also be potentially used as a hard template for synthesising other useful mesoporous materials. The aim of this research was to develop industrially feasible and environmentally friendly methods for the preparation of ordered mesoporous materials, to characterise these and to study their applications. The main techniques used for the characterisation of these mesoporous materials were N₂ physisorption, XRD and TEM. In the first part of the study, metal- and halogen-free ordered mesoporous polymer and carbon materials having 2D hexagonal (P6mm) and body centered cubic (Im3̅m) mesostructures were made using a modified two phase method employing alternative polymerisation and condensation catalysts. These materials had high surface area and pore volume and had narrow pore size distributions. Their physical evolution with increasing calcination temperature was examined as were the effects of varying synthesis parameters on the nature of the final mesostructure. The second part of the study was focused on the synthesis of ordered mesoporous ceria using metal- and halogen-free ordered mesoporous carbon materials - made in the first part of the study - as the hard template. The mesoporous ceria having 2D hexagonal arrangement of pores were successfully synthesised using a solid-liquid method which is a solvent free, easy to use and environmentally friendly method. The carbon template calcined at 400 °C was found to be the best template in terms of giving high loading of precursor and giving high quality product. The synthesis of body centered cubic ceria was less successful than hoped due to the small pore openings in this template material. The third part of study involved the preparation of mesoporous carbon supported Pd catalysts and their use in the hydrodechlorination of trichloromethane (TCM). The results were very promising, and 100 % conversions were obtained at 175 °C with high selectivity to alkanes and low selectivity to intermediate chlorinated products

Adsorption behaviour of Chrysoidine R dye on a metal/halide-free variant of ordered mesoporous carbon

The paper reports the removal of Chrysoidine R, a toxic mono-azo dye from its aqueous solution by employing metal- and halide-free variant of ordered mesoporous carbon as adsorbent in batch experiments. The influence of various parameters such as hydronium ion concentration, adsorbent dosage, initial dye concentration, exposure time on dye uptake was studied. The process could be described by Langmuir, Freundlich and Dubinin-Radushkevitch isotherm models. Evaluation of thermodynamic variables proved that the adsorption was spontaneous, feasible and endothermic. The kinetics involved in the process was worked out using pseudo-first-order and pseudo-second-order kinetic models. The latter was found appropriate for the analysis of the experimental data. The mechanism governing the overall adsorption was elucidated with the aid of various mathematical models. The adsorption was found to proceed via film diffusion with chemisorption being the rate-determining step. The complete removal of dye with fast removal rate makes the material propitious in the field of water treatment

Ordered mesoporous carbon as a support for palladium-based hydrodechlorination catalysts

Funding: University of St Andrews for a PhD scholarship (FS); FEDER/Ministerio de Ciencia, Innovación y Universidades – Agencia Estatal de Investigación / CTM2017-85498-R. C. Fernández Ruiz acknowledges MINECO for his research grant.Ordered mesoporous carbon (OMC) was employed as a support for palladium nanoparticles in catalysts for the gas phase hydrodechlorination (HDC) of trichloromethane (TCM). 1 wt% palladium was incorporated using three methods: incipient wetness (IW); a dilute solution (DS) method; and a solid-liquid (SL) method. The effect of the preparation method on catalyst structure and activity was investigated. Catalyst composition and nanostructure were studied using gas physisorption, high specification transmission electron microscopy and X-ray photoelectron spectroscopy. Catalytic conversion and product selectivities were determined in steady-state activity tests at temperatures between 70 and 300 °C. Two of the catalysts (IW and DS) showed excellent dispersion of fine Pd nanoparticles of average diameter ~2 nm. These materials showed excellent activity for HDC of TCM which compares favourably with the performance reported for Pd on amorphous carbon catalysts. In addition, they showed relatively high selectivities to the more valuable higher hydrocarbons. However, the SL method gave rise to catalysts with larger particles (~3 nm) and a less uniform palladium distribution. This resulted in lower conversion and lower selectivities to higher hydrocarbons and in more severe catalyst deactivation at the highest reaction temperatures.Publisher PDFPeer reviewe

Synthesis of mesoporous ceria using metal- and halogen-free ordered mesoporous carbon as a hard template

Authors thank the University of St Andrews for the PhD scholarship of FS. We acknowledge funding from MINECO/FEDER (Projects MAT2017-87579-R and MAT2016-81118-P) and from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 823717 –ESTEEM3.Ordered mesoporous cerias were synthesised by employing metal- and halogen- free ordered mesoporous carbons (OMCs) as the hard templates in a ‘nanocasting’ procedure. TEM, small angle (SA) and wide angle (WA) XRD, and N2 physisorption analyses were used to characterise the templates, intermediates and ceria products and electron tomography (STEM-HAADF) was used to explore the 3D morphology of the ceria nanostructures grown within the carbon templates. This allowed the relationships between the structures of the OMC templates and the products to be considered in detail as two parameters were varied. These were: the method of impregnation of the ceria precursor; and the temperature of calcination of the OMC template. Of the four impregnation methods tested, the solid-liquid method was found to be the most successful. This gave a high quality product with the highest yield of uniform mesopores, and crystalline nanorods of ceria arrayed in clear long-range order, as viewed by TEM and determined in SA and WAXRD. The specific surface area and pore volume exhibited by this sample were 111 m2/g and 0.39 cm3/g, respectively. 3D electron tomography reconstructions revealed the presence of a network of ordered, nanoscale, rod-like structures interlinked in a complex fashion. The effect of calcination temperature of the template on uptake of the ceria precursor during impregnation was studied by calcining OMCs at temperatures from 350 to 800 °C and using these as hard templates for the nanocasting of ceria. Of these, the carbon template calcined at 400 °C gave the highest quality product.Publisher PDFPeer reviewe