Hydrothermal Carbonization as Sustainable Process for the Complete Upgrading of Orange Peel Waste into Value-Added Chemicals and Bio-Carbon Materials

Abstract

In this study, a simple and green protocol to obtain hydrochar and high-added value products, mainly 5-hydroxymethylfurfural (5-HMF), furfural (FU), levulinic acid (LA) and alkyl levulinates, by using the hydrothermal carbonization (HTC) of orange peel waste (OPW) is presented. Process variables, such as reaction temperature (180–300 °C), reaction time (60–300 min), biomass:water ratio and initial pH were investigated in order to find the optimum conditions that maximize both the yields of solid hydrochar and 5-HMF and levulinates in the bio-oil. Data obtained evidence that the highest yield of hydrochar is obtained at a 210 °C reaction temperature, 180 min residence time, 6/1 w/w orange peel waste to water ratio and a 3.6 initial pH. The bio-products distribution strongly depends on the applied reaction conditions. Overall, 180 °C was found to be the best reaction temperature that maximizes the production of furfural and 5-HMF in the presence of pure water as a reaction medium.

Orange-Peel-Derived Nanobiochar for Targeted Cancer Therapy

“…A plausible mechanism of internalization of the DHF@NBC-B could be explained through the biotin-mediated interaction between DDS and cell membrane followed by the endocytosis of the DDS. In the same cell model, this internalization was previously observed by using similar carbon-based nanosized delivery systems [ 25 , 30 ]. The low amount of DHF loaded on the NBC-R system (4.1 wt%) did not allow us to compare higher drug concentrations, except by using very high concentrations of the DDS.…”

“…The nanostructured material to be used as biocompatible nanocarrier for targeted cancer therapy was synthesized by hydrothermal carbonization (HTC) of orange peels at 240 °C for 1 h. This green top-down synthetic method allows the graphitization of the carbon matrix starting from a natural renewable source, without the use of growth catalyst, thus avoiding impurities and additional cleaning procedures [ 30 , 31 ]. The synthesized carbonaceous material, obtained as previously reported by a series of deoxygenating processes from cellulose, hemicellulose and lignin, with 29% yield, has been shown to contain many oxygenated functionalities on the graphitized surface [ 30 , 31 ]. The biochar was treated with a NaOH 2 M solution and filtered through a 100 nm membrane filter.…”

“…The PL spectra clearly show quenching phenomena, which can be ascribed to the electron transfer process triggered by π–π stacking interactions between the phenyl ring of DHF and the p-cloud of NBC. This decrease in the fluorescence intensity together with the blueshift of conjugated samples from 539 nm (in the NBC-R sample) to 527 in the DHF@NBC-R and from 542 nm (in the NBC-B sample) to 532 in the DHF@NBC-B system, respectively, are indicative of the stable chemical interaction between the drug and the nanocarriers [ 30 ].…”

“…The general preparation procedure of hydrochar via HTC of orange peels was performed as previously reported [ 30 , 31 ]. Briefly, in a 300 mL stainless-steel autoclave under autogenous pressure and air atmosphere, 20 g of OP, reduced in small pieces, and 50 mL of deionized water were added, and the reactor was heated at 240 °C for 1 h at a stirring speed of 600 rpm.…”

“…In this work, we have synthesized fluorescent NBC in small size (<100 nm), endowed with graphene structure, by a simple HTC method and exfoliation procedure, starting from orange peel waste [ 30 , 31 ]. Then, in order to assess the possibility to use this nanomaterial as a smart nanocarrier for the targeted cancer cells delivery, different TL have been covalently conjugated to the graphene surface by means of a cleavable and biocompatible polyethylene glycol (PEG) linker [ 32 ].…”