Semiconducting zinc oxide (ZnO) is attracting lot of attention due to its unique properties such as direct wide band gap (3.37 eV) and large exciton binding energy (60 meV) at room temperature [1]. Due to these properties it has been studied extensively for making optical and electronic devices [1-3] like: light emitting diodes, solar cells, transducers, varistors, photodetetors, etc. Nanostructured ZnO can be synthesized by various methods such as physical, chemical, electrochemical, etc. but chemical route has attracted much attention due to the flexibility of controlling the shape and size of the structures by tuning the different growth conditions [4-10].

In recent years, the development of inorganic/polymer hybrid materials on nanometer scale have been receiving significant attention due to a wide range of potential applications in optoelectronic devices [11-13] and in field effect transistors [14]. The inorganic fillers at nanoscale exhibit high surface to volume ratio and thus expected to modify drastically the electrical, optical and dielectric properties of polymer. In general, the synthesis of hybrid of polymer/inorganic material has the goal of obtaining a new composite material having synergetic or complementary behaviors between the polymer and inorganic material. Polyaniline (PANi) is a most studied polymer because of its relative ease in preparation, good environmental stability [15,16] and tunable conductivity. Several reports on the synthesis of composite of nanofillers like: TiO₂, CdS, Na⁺-montmorillonite, Pd and Au with PANi have been demonstrated [17-21]. These synthesis processes have been carried out either in the aqueous solutions or via a sol-gel method, including the initial dispersion of the nanoparticles in the solution and the succedent oxidative polymerization of aniline with ammonium peroxidisulphate (APS). Since the conducting polyaniline and inorganic semiconducting material ZnO in nanoform both are having a wide range of technological applications, we got motivated to make composite of PANi and ZnO and believed to get novel properties resulting from the molecular level interaction of these two dissimilar chemical components [22,23].

In most of these cases, the nanocomposites were further used in various applications in their thin-film form. Although these PANi-ZnO nanocomposites are also conducting since they are polyaniline emeraldine chloride, their processability is still poor to limit their commercial uses although their conductivity could be measured by sandwiching the pellets. PANi doped with organic acids such as CSA, DBSA, PVSA etc. which possesses sufficiently strong Bronsted acid centers capable of polyaniline protonation together with suitable functional groups which, when introduced to the polymer matrix upon doping, induce the solubilization of its stiff conjugated backbone, is readily soluble, chemically stable, and electrically conductive [24-27].

There are few reports on the synthesis, morphological, electrical and optical studies [28,29] of PANi/ZnO composite. However to the best of our knowledge no study has been reported on effect of organic (ionic) acid doping on PANi/ZnO nanocomposite.

In this paper for the first time, we report systematic investigation on the effect of camphor sulfonic acid (CSA) doping on structural, morphological optical and electrical properties of PANi-ZnO nanocomposite. Much effort has been put into the investigation of the interaction between CSA and PANi-ZnO in order to gain a better understanding of the doping effect of CSA. The structural, morphological, optical and electrical properties of CSA doped PANi-ZnO nanocomposite were investigated using XRD, FTIR, SEM, UV-Vis spectroscopy and four probe technique.