Sulfonated Porous Polymeric Nanofibers as an Efficient Solid Acid Catalyst for the Production of 5-Hydroxymethylfurfural from Biomass Sujan Mondal, [a] John Mondal,* [b] and Asim Bhaumik* [a] Introduction Over a period of several centuries we, the people of the world, are modernized, globalized, and civilized. Energy is an issue that touches every person on the planet, because it is one of the primary needs of our existence. With the increase in the world population the gap between the supply and demand for energy is growing day by day. [1] On the other hand the fossil fuels are not renewable and hence their reserves are limited. Thus, our energy reserves are declining and this may cause a big problem in future if the issue remain unresolved for long. [2] Scientists have developed an alternative resource “bio- mass” to a viable fuel as an energy alternative. [3] Biomass-de- rived platform chemical 5-hydroxymethylfurfural (HMF) is now in widespread use. [4] HMF is an attractive molecule; it is a versa- tile and key intermediate of many industrially important chemi- cals and liquid fuels. For example, 2,5-furandicarboxylic acid, 2,5-bis(hydroxymethyl)furan and 2,5-bis(hydroxymethyl)tetrahy- drofuran are used as polyester building blocks. [5] The rehydrat- ed products of HMF, levulinic acid and formic acid, are also val- uable chemicals. Levulinic acid is a precursor of liquid fuel g- valerolactone, [6] 2,5-dimethylfuran another very demanding biofuel having very high energy density and insoluble in water [7] can be directly synthesized from HMF by means of hy- drogenesis or catalytic reduction. [8] With respect to the uncon- trolled CO 2 emission, people are more concerned about the global warming, and because of the rise of oil pricing research- ers are showing more interest in the synthesis of biofuels by biomass-conversion processes. [9] In the presence of an acid catalyst, carbohydrate sugars get converted mainly into HMF through dehydration. [10] Both Lewis acids as well as liquid mineral acids can catalyze these reac- tions. Many research groups have reported solid acid catalysts like zeolites, [10] metal chlorides, [11] phosphates/phosphonates/ graphene oxides, [12] and sulfuric acid/g-valerolactone [13] for the successful synthesis of HMF or other catalytic reactions. Highly corrosive and strong mineral acids like HCl, H 2 SO 4 , and H 3 PO 4 are often employed as catalyst for the HMF synthesis. [14] Solid acid catalysts have significant advantages over mineral acids because they are heterogeneous in nature, thus they are easily separable from the reaction mixture, nontoxic, noncorrosive in nature, recyclable, and diminishing other environmental prob- lems associated with mineral acids. High surface area and the presence of micropores/mesopores are the most crucial param- eters for the efficiency of these solid acid catalysts. A wide range of strategies have been developed to design porous ma- terials, which do not involve the use of templates or structure- directing agents. [15] In this context, porous organic polymers (POPs) are very demanding as one can tune the pore aperture and reactive functional groups, which are present as the build- ing blocks of the respective POPs. [16] A wide range of related porous polymeric materials such as porous aromatic frame- works, [17] conjugated microporous polymers, [18] porous organic Sustainable supply of energy is one of the biggest challenges today. The conversion of energy from any abundant and re- newable resources would be an ideal solution for this ever in- creasing demand of sustainable energy. Biomass provides a po- tential energy alternative through the platform chemical 5-hy- droxymethylfurfural (HMF), which is considered as a sustainable source for liquid fuels and commodity chemicals. Herein, we report the synthesis of a nanoporous polytriphenylamine (PPTPA-1) having high surface area (1437 m 2 g À1 ) by a simple one-step oxidative polymerization pathway. Upon sulfonation of PPTPA-1, the sulfonated polymer SPPTPA-1 showed very high surface acidity and it has been successfully employed as a solid acid catalyst for direct conversion of sugar to HMF. Both PPTPA-1 and SPPTPA-1 materials have distinct nanofiber mor- phologies and they are characterized thoroughly by using powder XRD, FTIR spectroscopy, 13 C solid state magic-angle- spinning NMR spectrometry, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and N 2 sorption techniques. We have optimized the HMF yields by using different carbohydrate sources and estimated the recycling efficiency of the catalyst. [a] S. Mondal, Prof. Dr. A. Bhaumik Department of Materials Science Indian Association for the Cultivation of Science 2A and 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700 032 (India) E-mail : msab@iacs.res.in [b] Dr. J. Mondal Inorganic and Physical Chemistry Division CSIR-Indian Institute of Chemical Technology (IICT) Uppal Road, Hyderabad 500007 (India) E-mail : johncuchem@gmail.com Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201500709. ChemCatChem 2015, 7, 3570 – 3578 # 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3570 Full Papers DOI: 10.1002/cctc.201500709