decreasing diameter of the nano-adsorbent. If the value is negative, then the molar entropy increases. However, this may not necessarily be the case for the molar enthalpy; if the value is negative, then the effect of the nano-adsorbent diameter on the molar enthalpy depends on the value of ð@r1P =@TÞp ð@rN=@TÞp, relative to r1P rN; which is determined by the nanoadsorption system.
Similarly, the thermodynamic relations based on the effect of particle size on nanoadsorption in the gas phase can be obtained.
3. Experimental section
3.1. Materials
Copper sulfate anhydrous and silver nitrate supplied by Beijing Chemical Works were of analytical reagent grade. Nano-sized zinc oxide (nano-ZnO) and nano-sized titanium dioxide (nano-TiO2) were prepared by homogeneous precipitation methods in our laboratory. The source and purity of chemical samples used are given in table 1.
3.2. Analysis of nanoparticles
X-ray diffraction analyses of the samples were carried out via a powder X-ray diffractometer (Shimadzu 6000, Japan) using copper radiation (figure 1). The main diffraction peaks of the samples matched well with the nano-ZnO crystal (JCPDS: 89-0511) and the nano-TiO2 crystal (JCPDS: 89-4921). Mean diameters of the samples were calculated using the Scherrer formula based on the half peak width of the characteristic diffraction peaks [15–17].
3.3. Adsorption experiments
A copper sulfate solution with a known initial concentration was poured into a beaker flask with a copper electrode and a reference electrode, which was placed in a thermostatic bath. After the temperature equilibrated, nano-ZnO powder was added into the beaker flask