Effect of successive recycling and reuse of acid liquor for the synthesis of graphene oxides with higher oxygen-to-carbon ratios

Mohammad Amirul Hoque; A F M Mustafizur Rahman; Mohammad Mahbubur Rahman; Mohammad Nazrul Islam Bhuiyan; Shirin Akter Jahan; Md Aftab Ali Shaikh; Mohammad Nurnabi

doi:10.1016/j.heliyon.2024.e27639

Effect of successive recycling and reuse of acid liquor for the synthesis of graphene oxides with higher oxygen-to-carbon ratios

Heliyon. 2024 Mar 9;10(6):e27639. doi: 10.1016/j.heliyon.2024.e27639. eCollection 2024 Mar 30.

Authors

Mohammad Amirul Hoque¹, A F M Mustafizur Rahman², Mohammad Mahbubur Rahman¹, Mohammad Nazrul Islam Bhuiyan³, Shirin Akter Jahan⁴, Md Aftab Ali Shaikh^{1

5}, Mohammad Nurnabi²

Affiliations

¹ BCSIR Dhaka Laboratories, Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhanmondi, Dhaka, 1205, Bangladesh.
² Department of Applied Chemistry and Chemical Engineering, University of Dhaka (DU), Dhaka, 1000, Bangladesh.
³ Institute of Food Science and Technology, Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhanmondi, Dhaka, 1205, Bangladesh.
⁴ Institute of Glass and Ceramic Research and Testing, Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhanmondi, Dhaka, 1205, Bangladesh.
⁵ Department of Chemistry, University of Dhaka (DU), Dhaka, 1000, Bangladesh.

Abstract

Graphene has recently drawn exponential attention due to its surprising physicochemical properties and diversified field of applications. Although graphene oxides (GOs), itself is an exclusive material, it is also an intermediate product for the production of reduced graphene oxides (rGOs), graphene and their derivatives, which are other more superficial materials. In this study, GOs with higher oxygen to carbon ratios were synthesized following the Tour method, where the excess feed acid liquor (FAL) of mixed concentrated sulfuric and orthophosphoric acids at a ratio of 90:10 was recovered from the reaction slurries by applying the centrifugation technique. About 80-90 % of the FAL was recycled and reused as feed for the subsequent batches. The changes in the properties of FAL for the five consecutive recycling and reuse were studied. The properties of recycled FALs were investigated by measuring density, moisture content, pH, and ion concentration. The consecutive recycling of FALs tends to increase the moisture content about 0.5% in each recycles. Ion-chromatography (IC) was used to measure the variation in SO₄^2- and PO₄^3- ions in the FALs. The H₂SO₄ reacts with KMnO₄ and crystalized out from the recovered FAL faster than the phosphoric acid. So, sulfuric acid content in the makeover FALs must be greater than primary FAL. The product GOs were characterized using FT-IR, FT-Raman, UVVis, STA, SEM, XPS, Zeta-potential, and particle size analyzers. The variation of the properties of GOs with the changes in the reaction parameters such as temperature and time were investigated and correlated with the product yield. It was observed that the effect of temperature on the reaction rate was found to be negatively and positive with the reaction time. The oxygen-to-carbon atomic ratio from XPS analysis was found 66.7%, which supported the increase in product yields 66.9% in the experimental results. The effect of acid concentration, reaction temperature, and time on the GOs properties were satisfactory, correlated, and easily controllable with the reaction conditions. A higher extent of oxidation and enhanced product yields 65-70% were observed at 60-70 °C and 14-18 h. A mixture of nano- and macro-molecular GOs was obtained, and their compositions were easily controllable and separable by controlling the reaction conditions. A correlation was made among the properties of synthesized GOs, FAL, and recycled FAL and reaction conditions.

Keywords: Acid recovery; Acid reuse; Chemical oxidation; Graphene; Graphene oxides; Reduced graphene oxides.