j.cej.2015.04.032
Comparative study of oxidation of benzyl alcohol: Influence of Cu-doped metal cation on nano ZnO catalytic activity
 Pure ZnO was prepared through hydrolysis and oxidizing process. Zn(NO3)2 (1 mmol) dissolved in 100 mL of distilled water with continuous stirring. NaOH solution was added into the drop by drop until the pH of the solution became 12. The resulting white particles were washed three times with distilled water and dried for 24 h at 80 degC. At this point, the white product did not show high crystallinity since it consisted of ZnO and Zn(OH)2. Calcining at 500 degC for 1 h was necessary to obtain high crystalline ZnO [30]. 
Synthesis of CuxZn1-xO (1% Cu-doped) nanopowder was carried out using a modified procedure [23] and [24]. The targets were specifically designed using high purity Zn(NO3)2*6H2O (99.99%) and CuSO4*5H2O (99%) powders. The Cu-doped ZnO catalyst was prepared by a two-step procedure: (1) preparation of the precursor by co-precipitation; (2) formation of the Cu/ZnO nanopowder by thermal decomposition. This method has been considered to be efficient and inexpensive, allowing for the production of high purity, homogeneous, and fine crystalline powders. 
Stoichiometric quantities of Zn and Cu salts were dissolved in 100 mL of deionized double distilled water (solution A). Separately, a solution was prepared by dissolving appropriate amounts of NaOH and Na2CO3 in deionized double distilled water (solution B). Solution A was heated to 85 degC and solution B was added dropwise into it with constant stirring. The temperature was maintained at 85 degC and the reaction mixture was stirred for 1 h and refluxed through a water condenser. The resulting solution was cooled to room temperature and the green precipitate that formed was washed with 3 x 20 mL of de-ionized water and dried under vacuum overnight at 50 degC. Finally, the precursors were calcined at 450 degC for 90 min in a muffle furnace under air atmosphere to obtain the nanocrystalline Cu/ZnO powder.
distilled water
100 mL
mL
Zn(NO3)2
dissolved
1 mmol
mmol
solution
pH
12
resulting white particles
dried
24 h
h
resulting white particles
dried
80 degC
degC
resulting white particles
washed
three times
times
ZnO
Calcining
500 degC
degC
ZnO
Calcining
1 h
h
Cu-doped
1%
%
high purity Zn(NO3)2*6H2O
powders
99.99%
%
CuSO4*5H2O
powders
99%
%
deionized double distilled water (solution A)
100 mL
mL
Solution A
heated
85 degC
degC
reaction mixture
stirred
1 h
h
reaction mixture
temperature
85 degC
degC
de-ionized water
3 x 20 mL
mL
precursors
calcined
450 degC
degC
precursors
calcined
90 min
min
green precipitate that formed
dried under vacuum overnight
50 degC
degC