Milli q gradient water filtration system

Lithium cobalt oxide (LCO,
99.9%), N-methyl urea (NMU, 97%), acetamide (A, 99%),
urea (U, ACS reagent), N,N′-dimethylurea
(NN′DMU, 99%), N-methylacetamide (NMA, 99%), N-methyl-2-pyrrolidone (NMP), potassium nitrate (ACS reagent),
nitric acid, methanol (HPLC grade), and acetic acid (glacial) were
all purchased from Sigma-Aldrich and used without any purification
process unless otherwise mentioned. Gold-coated silicon wafers were
purchased from Sigma-Aldrich. NMU was recrystallized from methanol.
Ultrapure-grade water (resistivity 18.2 MΩ), purified using
the Milli-Q gradient water filtration system (Millipore), was used
for all purposes wherever necessary. Prior to usage, the Au thin films
were immersed in a piranha solution (3:1, H₂O₂ (30%)/H₂SO₄ (conc.) v/v) for 30 s, washed with 5 mL of water five times (fresh
water was replaced each time), dried flushed with N₂ and
immediately used for analysis.

Acetamide (A), urea (U), N-methylacetamide (NMA), N-methylurea (NMU), N,N′-dimethylurea (NN’DMU) and N,N-dimethylurea (NNDMU) (see Scheme S1 in ESI), methacrylic acid (MAA), 1,4-bis(acryloyl)piperazine (BAP), 2,2′-azobis(2-methylpropionamidine) dihydrochloride (ABAH), potassium chloride, silica gel were all purchased from Sigma-Aldrich (Steinheim, Germany) and stored in vacuum desiccator. MAA was vacuum distilled and stored at 4 °C. ABAH was recrystallized in acetone–water mixture (1:1, v/v). Methanol, acetone and chloroform were of analytical grade obtained from Chemtronica (Stockholm, Sweden) and dried over 4 Å molecular sieves. De-ionized water (resistance value < 18.2 MΩ) collected from a Milli-Q gradient water filtration system (Millipore, MA, USA), was used in this study.

Iron (III) chloride hexahydrate (FeCl₃·6H₂O), iron (II) chloride tetrahydrate (FeCl₂·4H₂O), sodium dodecyl sulphate (SDS) and tetraethylorthosilicate (TEOS) were purchased from Sigma Aldrich (Steinheim, Germany). Sodium acetate, polyEthylene glycol 6000 (PEG) and ammonia solution (25%) were from VWR chemicals BDH (Leuven, Belgium), Fluka Biochemica (Buchs, Switzerland) and Merck (Darstadt, Germany) respectively. Ethylene glycol, acetone and absolute ethanol (EtOH) were obtained from Carlo Erba Reagents (Barcelona, Spain). Deionized water (18.2 MΩ) acquired from a Milli-Q gradient water filtration system (Millipore, Burlington, MA, USA) was used for solution preparation, rinsing and extraction purpose.