# Doped Zinc Oxide Nanoparticles: Synthesis, Characterization and Potential Use in Nanomedicine
## 3 Synthesis Methods and Characterization
### Wet Chemical Methods
A change in the unit cell parameters was observed in a large variety of works in which ZnO was doped, as it has been summarized in Table 1.  
In the work of [PERSON] et al., gadolinium (III) nitrate hexahydrate was used as a doping precursor as well [177]. Different levels of Gd doping were considered and the photocatalytic properties of Gd-doped \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & **Dopant** & **Doping** & \multicolumn{2}{c}{**(Ox. State)**} & & & **Unit** \\  & **Element** & **Doping** & **Ionic Radius** & \(a\) & \(a_{D}\)-\(a_{0}\)1 [FOOTNOTE:1]Footnote 1: Relative variation of parameter a of doped ZnO (\(a_{0}\)) with respect to the pure counterpart evaluated in the paper (\(a_{0}\)). 2 Relative variation of parameters of doped ZnO (\(c_{0}\)) with respect to the pure counterpart evaluated in the paper (\(c_{0}\)). 2 Relative variation of parameters of doped ZnO (\(c_{0}\)) with respect to the pure counterpart evaluated in the paper (\(c_{0}\)). & **Cell** \\  & & & & & & **Volume** \\ \hline
[170] & Bulk & - & (+2) 74 & 3.2500 Å & & 5.2047 Å & - & 47.609 Å\({}^{3}\) \\
[116] & La & 5\% mol & (+3) 103 & 3.2497 Å & \(-1.3\times 10^{-3}\) Å & 5.2058 Å & \(-3.0\times 10^{-3}\) Å & 47.610 Å\({}^{3}\) \\
[171] & Ce & 1\% mol & (+3) 101 & 3.2503 Å & \(-1.6\times 10^{-3}\) Å & 5.2058 Å & \(-6.2\times 10^{-3}\) Å & 47.629 Å\({}^{3}\) \\  & & (+2) 129, (+3) & 3.2495 Å & \(12.9\times 10^{-3}\) Å & 5.2058 Å & \(20.7\times 10^{-3}\) Å & 47.605 Å\({}^{3}\) \\
[150] & Eu & 5\% mol & (+2) 117, (+3) & 3.251 Å & \(2.0\times 10^{-3}\) Å & 5.209 Å & \(4.0\times 10^{-3}\) Å & 47.693 Å\({}^{3}\) \\
[157] & Gd & 5\% mol & (+3) 93 & 3.2735 Å & \(20.6\times 10^{-3}\) Å & 5.2128 Å & \(2.6\times 10^{-3}\) Å & 48.375 Å\({}^{3}\) \\  & & & (+2) 79, (+3) & & & & \\
[173] & V & 5\% mol & 64, & 3.2522 Å & \(0.5\times 10^{-3}\) Å & 5.2075 Å & \(-1.0\times 10^{-3}\) Å & 47.699 Å\({}^{3}\) \\  & & (+4) 58, (+5) 54 & & & & & \\
[126] & Mn & 5\% at. & (+4) 21 & (+3) 72 & 3.2502 Å & \(2.2\times 10^{-3}\) Å & 5.2093 Å & \(3.0\times 10^{-3}\) Å & 47.710 Å\({}^{3}\) \\  & & (+4) 67, (+7) 60 & & & & & & \\
[174] & Fe & 5.09\% & (+2) 75, (+3) 69 & 3.2536 Å & \(2.3\times 10^{-3}\) Å & 5.2093 Å & \(11.1\times 10^{-3}\) Å & 47.757 Å\({}^{3}\) \\
[175] & Co & 5\% mol & (+2) 79, (+3) 68 & 3.2503 Å & \(-2.0\times 10^{-3}\) Å & 5.2059 Å & \(-0.8\times 10^{-3}\) Å & 47.629 Å\({}^{3}\) \\
[176] & Cu & 5\% at & (+1) 91, (+2) 87 & 3.2494 Å & \(-0.2\times 10^{-3}\) Å & 5.2054 Å & \(-0.4\times 10^{-3}\) Å & 47.598 Å\({}^{3}\) \\
[152] & Ag & 5\% mol & (+1) 129, (+2) & 3.2579 Å & \(3.6\times 10^{-3}\) Å & 5.2220 Å & \(3.7\times 10^{-3}\) Å & 48.000 Å\({}^{3}\) \\
[144] & Li & 5\% at & (+1) 90 & 3.225 Å & \(-30\times 10^{-3}\) Å & 5.162Å & \(-50\times 10^{-3}\) Å & 46.495 Å\({}^{3}\) \\
[138] & Mg & 5\% mol & (+2) 86 & 3.2585 Å & \(-3.6\times 10^{-3}\) Å & 5.2181 Å & \(-7.5\times 10^{-3}\) Å & 47.982 Å\({}^{3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Doped ZnO structural properties. ZnO nanoparticles were evaluated. The nanoparticles synthesized in this work, whose electron microscopy images are reported in Figure 4--seen in the bottom panel--were obtained through a co-precipitation method in which the metal precursors were first mixed together at a proper ratio and then NaOH was added to allow the precipitation of the particles. In this case, after the synthesis, the obtained samples were also calcined at 500 \({}^{\circ}\)C for 2 h. The XRD pattern of the resulting samples (Figure 4, top left panel) showed that 5 mol.% Gd-doped ZnO nanoparticles presented a secondary phase. Therefore, this level of Gd doping can be assumed as the Gd\({}^{3+}\) solubility limit for this synthesis. Fourier transform infrared spectroscopy (FTIR) was also carried out (Figure 4, top right panel) and it evidenced that the peak associated with the Zn--O bond (443 cm\({}^{-1}\)) was broader in the doped ZnO nanoparticles, due to the deformation of the lattice.