First, sodium tungstate (Na2WO4*2H2O) (0.005 mol), hydroxylamine hydrochloride (NH2OH*HCl) (0.01 mol), sulfourea (CH4N2S) (0.02 mol) were dissolved in 30 ml deionized water. The surfactants were then added into the solution under constant stirring. The pH value of the mixture was adjusted to 6 by dropping 2 mol/L hydrochloric acid (HCl) or ammonia water (NH3*H2O). The final solution was transferred into a 50 ml Teflon-lined stainless steel autoclave, which was sealed and treated at 180 degC for 24 h. After calcination, the as-prepared samples were washed several times with distilled water and absolute ethanol, and dried in air at 60 degC for 10 h. To better describe the samples, the precipitates using no additive was named sample I, while powders obtained with the addition of CTAB (0.18 g, 0.24 g) and PEG (0.18 g ) were named as sample II, III and IV, respectively, as shown in Table 1.
sodium tungstate (Na2WO4*2H2O)
dissolved
0.005 mol
mol
hydroxylamine hydrochloride (NH2OH*HCl)
dissolved
0.01 mol
mol
sulfourea (CH4N2S)
dissolved
0.02 mol
mol
deionized water
30 ml
ml
mixture
pH value
6
hydrochloric acid (HCl) or ammonia water (NH3*H2O)
dropping
2 mol/L
mol/L
Teflon-lined stainless steel autoclave
50 ml
ml
final solution
treated
180 degC
degC
final solution
treated
24 h
h
as-prepared samples
dried in air
60 degC
degC
as-prepared samples
dried
10 h
h