Novel Insights into the Structure and Reduction of Graphene Oxide: A Case of Thiourea

In this work, samples of reduced graphene oxide (rGO) were prepared by treating graphite oxide (GrO) with thiourea (TU) and ascorbic acid (AA). Aerogels rGO-TU and rGO-AA were prepared using the freeze-drying method and were analyzed using X-ray diffraction, FTIR and Raman spectroscopy, ¹H and ¹³C NMR, TEM, and SEM-EDS. Based on the NMR, FTIR, SEM-EDS, and TEM data, GO with TU is reduced with simultaneous functionalization of its oxygen-containing groups. According to ¹H and ¹³C NMR data, the reduction of GO occurred simultaneously with an interaction of the amino groups of thiourea with carbonyl groups on the graphene sheets, forming an imine bond. This is evidenced by the appearance of additional signals in the ¹³C spectrum of GO-TU samples in the region of 140-230 ppm. The Boehm titration method showed that the number of oxygen-containing groups in rGO-TU aerogels decreased by about five times compared to GO. However, thiourea interacts with the GO surface, most likely due to electrostatic interaction and hydrogen bonds. The adsorption capacity of rGO-TU aerogel with respect to methylene blue (MB) after 1440 min was 60.2 mg/g, while for rGO-AA it was 71.4 mg/g. This fact indicates the importance of optimizing GO reduction to increase the number of active sites.