Hydrofluoric acid hf

Titanium (Ti) foil, dimethyl sulfoxide (DMSO), chloroauric acid hydrate (HAuCl₄·H₂O), sodium citrate (Na₃C₆H₅O₇), sodium borohydride (NaBH₄, 98%), chitosan (crab shells), acetic acid (CH₃COOH, 99%), sodium phosphate monobasic (NaH₂PO₄, 99%) and sodium phosphate dibasic (Na₂HPO₄, 99%), sodium hydroxide (NaOH) pellet, hydrochloric acid (HCl), and hydrogen peroxide (H₂O₂, 30 wt%) were purchased from Sigma-Aldrich (St. Louis, MI, USA). Hydrofluoric acid (HF, 49%) was purchased from Fisher Chemical (Waltham, MA, USA). The Difco™ Lactobacilli MRS Agar and Lactobacilli MRS broth were purchased from Merck Millipore (Darmstadt, Germany). H₂O₂ was preserved at 4 °C. Ultrapure water (18 MΩ·cm) purified with a Nanopure^® water system (Merck, Germany) was used to prepare all experiment solutions. All the reagents were of analytical grade.

In the synthesis of carbons, sucrose (Carlo Erba), tetraethyl orthosilicate (TEOS) (Acros Organics), triblock copolymer (Pluronic P123 MW = 5800, Sigma Aldrich), n-butanol (VWR Chemicals), and sulfuric acid (H₂SO₄) (Fluka) were used as the carbon source, silica source, structure directing agent, cosolvent, and catalyst, respectively. Hydrochloric acid (HCl) (Merck) was used to provide the acidic medium and hydrofluoric acid (HF) (Fisher Chemical) was used to remove silica. All of the chemicals used in the study were analytical grade and they were used as received.

Sediment samples were first pre-grinded, sieved through 2-mm sieves and homogenized. Sub-samples of 0.25 g were accurately weighed using an analytical balance, 10 mL of conc. Hydrofluoric acid (HF, 47–51%, Fisher Chemicals, Waltham, MA, USA, Trace Metal Grade) was added and the mixtures were left for 24 h. Subsequent dissolution was performed using a sand bath after adding an additional amount of 10 mL conc. HF (47–51%, Fisher Chemicals, Waltham, MA, USA, Trace Metal Grade) and 5 mL conc. Perchloric acid (HClO₄, 70% Fisher Chemicals, Waltham, MA, USA, Trace Metal Grade). The samples were heated until the acid mixture was reduced to 1/3 of the initial volume. Then portions of 10 mL conc. HF were added and heating in a sand bath was performed until complete dissolution of the sediments. Then two portions of 10 mL conc. Nitric acid (HNO₃, 67–69%, Fisher Chemicals, Waltham, MA, USA, Trace Metal Grade) were added and the samples were heated in a sand bath until the volume was reduced to 0.5–1 mL. After cooling, the samples were quantitatively transferred to 50 mL polyethylene tubes by repeated washing with double deionized water. All samples were initially diluted to 50 mL, and immediately before instrumental measurement, an additional dilution of 1 mL to 14 mL was performed.