5-Hydroxymethylfurfural (HMF), an organic platform chemical, used as a precursor of various industrial chemicals, was synthesized from waste coffee grounds (WCG), glucose, and fructose, using Al­(NO3)3 and H2SO4 as catalysts, in a highly aqueous binary solvent system consisting of water and dimethyl sulfoxide (DMSO) and a conventional microwave as the heating system. The effect of tuning the water/DMSO ratio was first studied. Results showed that the highest HMF yield can be obtained using 6:4, 5:5, and 7:3 water/DMSO ratios for WCG, glucose, and fructose, respectively. A response surface methodology was also employed to determine the interactions among catalyst loading, reaction time, and microwave power and their effects HMF yield. Yields of up to 13.65% (WCG), 28.50% (glucose), and 60.8% (fructose) were observed. This study demonstrates the use of WCG as an HMF precursor and the tuning of several experimental factors to increase the HMF yield from simple sugars and WCG.

Biologically derived carbon-based nanomaterials have been gaining attention in the recent years due to its various potential medical applications. In this study, fluorescent carbon nanoparticles (FCNPs) derived from an abundant alga, Cladophora vagabunda, is first reported. FCNPs with an average diameter of ~43 nm was synthesized via hydrothermal process, a simple and green method. The synthesized FCNPs exhibited absorbances in the ultraviolet to visible regions and emissions at 600 and 650 nm. Phytochemical screening and bioactivity tests were conducted to determine various bioactive compounds present in the FCNP surface and its antibacterial, antioxidant, and cytotoxic properties. Results showed that FCNPs from C. vagabunda contains tannin, saponin, flavonoids, and phenolic compounds which are known for their antimicrobial property as supported by the result of agar well diffusion method using a Gram-positive S. aureus and Gram-negative E. coli. Moreover, FCNPs shows inactive cytotoxicity using brine shrimp lethality test at ratio as high as 1:1 in 40% (v/v) ethanol. The results suggest the potential use of FCNPs from C. vagabunda as a fluorescent material with various biological activities.

The increasing oil demand and exhaustion of reserves have initiated stimulus to search for new and sustainable sources of fuels and fine chemicals. Lignocellulosic biomass turned out to be a promising and renewable feedstock for these applications. 5-hydroxymethylfurfural (HMF) is one of the most promising building blocks for bio-based chemicals that can be derived from lignocellulosic biomass which can be potentially applied for large scale production. However, one of the main factors holding its transition is the need for sustainable, green and financially feasible processes. This review provides the studies made towards catalytic systems used for HMF production, as well as the various solvents and heating system applied. Research efforts to unravel the interactions among catalysts, solvents, and heating systems are encouraged, thereby engineering a synergistic conversion system for biomass valorization.