Ammonium persulphate

The bromine-doped graphene was transferred on to standard lacey carbon Cu TEM grids for TEM and HRTEM studies. For that purpose, first the copper substrate was spin-coated with a PMMA solution in ethyl acetate, followed by its etching in 0.5 molar aqueous solution of ammonium persulphate (Sigma Aldrich, purity ≥ 98%) for ∼100 minutes. Thereafter it was rinsed thoroughly in deionized water. The film was then fished in deionized water onto a standard lacey carbon Cu TEM grid. The PMMA coating was removed in hot acetone vapor.^{25 (link)} Finally, to remove any organic residue that might have lifted, the TEM grid was annealed in high vacuum (10⁻⁶ mbar) at 200 °C for 12 hours.^{26 (link)}For SEM and Raman characterizations, instead of a TEM grid SiO₂ (300 nm)/Si wafer was used as the substrate for transfer. The wafer was sonicated in pure acetone followed by washing in absolute ethanol and then drying in N₂. The graphene film was fished onto it and then annealed in an oven at 75 °C for 20 minutes. Afterwards, PMMA was removed by dipping it (for 2 minutes) in pure acetone.

Polyethylene glycol (PEG 6000), ammonium sulphate, sodium chloride, lysozyme, horse radish peroxidase, α-chymotrypsinogen A, acrylamide, ovalbumin, bovine serum albumin, N,N,N¹,N¹-tetramethylethylenediamine (TEMED), ammonium persulphate, sodium dodecyl sulphate (SDS), Coomassie brilliant blue R-250, sodium alginate, glutaraldehyde and 3,4-dihydroxyphenyl-L-alanine (L-DOPA), were obtained from Sigma Chemical Company, St Louis, USA. Protein markers for SDS-PAGE were obtained from Carl Roth, Karlsruhe, Germany. Sephadex G-100 was obtained from GE Healthcare Bio-sciences (GHB), Uppsala, Sweden. Other reagents used were of analytical grade.

Silica extracted from diatomaceous earth in our previous study was used after drying.^22,23 Sodium dodecyl sulphate, 3-bromo-1,2-benzenediamine, urea and ammonium persulphate were of analytical grade and obtained from Sigma-Aldrich (St Louis, USA), NaOH and HCl was obtained from Rochelle Chemicals (Johannesburg, South Africa). Milli-Q water from Millipore S.A.S (Molsheim, France) (18.2 μs cm⁻¹ at 25 °C) was also used in all dilutions. Tea bags were bought from Shoprite, Thohoyandou, South Africa. Vacuum pump oil was from Telstar technologies (Barcelona, Spain). Freeze dryer (Telstar Lyoquest-55, Shanghai, China) was used to freeze dry samples and spectroquant UV spectrophotometer (Merk Group, Germiston, South Africa) was used for total organic carbon measurement and Stuart reciprocating shaker (Staffordshire, UK) was used for shaking and functional group analysis was carried out using an ALPHA FT-IR spectrophotometer from Bruker Pty (Sandton, South Africa).
Synthetic oily wastewater (SOWW) was prepared by modifying the method described by Shoba et al.^{24 (link)} Sodium dodecyl sulphate and Vacuum pump oil (90 : 1 v/w) were added to a 1 L flask and the volume made up with water. The mixture was then sonicated for 5 min at an amplitude of 75% and cycle of 0.5 to make the mixture homogenous.