Effect of Process Parameters on the Graphite Expansion Produced by a Green Modification of the Hummers Method

Abstract

Adsorption stand out among other standard techniques used for water treatment because of its remarkable simplicity, easy operation, and high removal capability. Expanded graphite has been selected as a promising agent for oil spill adsorption, but its production involves the generation of corrosive remnants and massive amounts of contaminated washing waters. Although the advantageous use of the H2O2–H2SO4 mixture was described in 1978, reported works using this method are scarce. This work deals with the urgent necessity for the development of alternative chemical routes decreasing their environmental impact (based on green chemistry concepts), presenting a process for expanded graphite production using only two intercalation chemicals, reducing the consumption of sulfuric acid to only 10% and avoiding the use of strong oxidant salts (both environmentally detrimental). Three process parameters were evaluated: milling effect, peroxide concentration, and microwave expansion. Some remarkable results were obtained following this route: high specific volumes elevated oil adsorption rate exhibiting a high oil–water selectivity and rapid adsorption. Furthermore, the recycling capability was checked using up to six adsorption cycles. Results showed that milling time reduces the specimen’s expansion rate and oil adsorption capacity due to poor intercalant insertion and generation of small particle sizes.

The potential of thermally expanded graphite in oil sorption applications

“…However, its production and regeneration can be quite expensive. 9 Similarly, special molecules such as carbon nanotubes and graphene have demonstrated exceptional performance, but their current cost renders them impractical for utilization in oil spill remediation. 12 The intrinsic properties of expanded graphite, including its low density, high porosity, and electrical conductivity, have received signicant global attention for their potential applications.…”

“…This uniform heating feature of microwave irradiation contributes to the consistent and controlled expansion of GICs. 9,44 When exposed to a signicant thermal shock up to 1000 °C or excessive heating, such as in a domestic microwave oven, graphite bisulfate undergoes irreversible expansion along the caxis. This expansion can reach hundreds of times the original size.…”

“…117 (2) Heating rate: high-temperature preparation usually involves slower heating rates to ensure controlled expansion, while microwave irradiation allows for rapid and selective heating, leading to faster expansion. 9,52 (3) Energy efficiency: microwave irradiation is generally more energy-efficient than high-temperature methods. Microwaves directly heat the intercalated graphite, reducing energy loss to the surrounding environment.…”

“…Microwave irradiation, on the other hand, may result in faster and sometimes less controllable expansion due to rapid and intense heating. 9 (5) Scale and throughput: high-temperature methods are oen more suitable for large-scale production due to the availability of larger furnaces and ovens. Microwave irradiation, although capable of producing expanded graphite, may have limitations in terms of batch size and throughput.…”

“…Various materials have been employed in endeavours to restore marine and wildlife habitats, although with varying degrees of success, in the context of oil spill cleanup and recovery. [8][9][10] 1.1 Oil spills remediation Various techniques are used to tackle the oil spills which include mechanical, physical, biological, and physic-chemical methods. The mechanical technique involves the use of specialized mechanical devices, known as "skimmers," that have been effectively designed and deployed on oating platforms to collect substantial oil layers from the water's surface.…”