In this research project, in order to prevent the agglomeration and better dispersion of zinc oxide nanoparticles (ZnO ) in the polymeric matrix, their surface was modified with folic acid (FA) as a biomolecule. This process was performed under ultrasonic irradiations as a biocompatible, inexpensive and fast method. The properties of ZnO-FA were identified and examined using different methods including Fourrier transform infrared microscopy (FT-IR), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and thermal gravimetry analysis (TGA). The results of the FT-IR and EDX spectra showed successful modification of the ZnO with FA. Also increasing the size of the ZnO that was obtained from the TEM images, as well as the results of TGA confirmed the presence of FA on the surface of ZnO . Poly(vinyl alcohol) nanocomposite films (PVA NC films) containing different percentages of ZnO-FA (2, 5 and 8 wt%) were prepared by ultrasonic waves. Different methods such as FT-IR, UV-Vis, XRD, FE-SEM, TEM, TGA, EDX and mechanical test were used to identify and investigate the prepared NC films. TGA results showed better thermal stability for NC films. The histogram and the normal distribution curve for TEM images of PVA/ZnO-FA NC film 5 wt% exhibited a uniform and effective distribution of the ZnO-FA in the PVA matrix. The antibacterial activity of PVA/ZnO-FA NC film 8 wt% was investigated and the results showed that the NC film stopped the growth of bacteria very well. In the following, crosslinked PVA/ZnO-FA NC film 2 wt% was prepared for the removal of Congo red (CR) from aqueous solution and was crosslinked with glutaraldehyde (GA) as a crosslinker agent in order to be insoluble in an aqueous solution. Efficient factors on the adsorption process such as pH, adsorbent dosage, time, initial concentration of dye and temperature were investigated. The adsorption process showed a high dependence on the pH value, and the result showed that the interaction between the adsorbent and dye may follow different mechanisms such as hydrogen bonding, ?-? interactions, and so on. Investigating the kinetic models showed that the rate of absorption process was controlled by more than one mechanism. But the experimental data matching with the nonlinear pseudo-second order model which confirms the chemical adsorption process. An investigation of the isotherm models showed that the data were more consistent with linear Langmuier isotherm and the adsorption mechanism was of physical type. Thermodynamic data showed that the adsorption of CR by the adsorbent is an exothermic process with decreasing entropy. The results generally described the likelihood of physical and chemical adsorption simultaneously for the adsorption mechanism.