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A series of acrylic‐based cationic polyelectrolyte nanocomposites including water‐soluble monomers acrylamide (AAm) and 2‐acryloyloxyethyltrimethylammonium chloride (DAC) with different mole percent of DAC (30, 40, and 45%) in feed were produced using TiO2 nanoparticles (0.018, 0.037, and 0.11 wt%) as photoinitiator in the aqueous solution of monomers and named as p(ADT)1–9. The LED light at 365 nm was used for photocatalysis activation of TiO2 nanoparticles. Structure and morphology of the synthetic polyelectrolyte were characterized by FT‐IR, NMR, TGA, FESEM‐EDX, and TEM. The other properties of synthetic polyelectrolyte such as molecular weight, viscosity, charge density, AAm/DAC molar ratio in copolymers, reactivity ratio values for the AAm and DAC monomers, and polymerization degree were measured. Furthermore, coagulation performance of these polyelectrolytes was investigated in soil suspension (1,000 ml, initial turbidity = 1,715 NTU). The prepared nanocomposites enhanced the coagulation of soil suspension up to 99.5% in low dosages. The best turbidity removal efficiencies (TRE) between 99.5–99.77% were achieved by p(ADT)3 conatining 30% DAC and 0.11 wt% TiO2. Decreasing the temperature from room temperature to 0°C led to an increase in TRE from 98 to 99.8%. Also, increasing the pH from 4 to 12 led to a decrease in TRE from 99.86 to 94%.

To study the effect of cationic polyelectrolytes on the photoreduction of nitrobenzene over TiO2, a sequence of synthetic cationic polyelectrolytes (SCPs) containing acrylamide (AAm) and 2‐(dimethylamino)ethyl acrylate methochloride (DAEA) using various AAm:DAEA molar ratios (50:50, 55:45, 60:40, 70:30, and 85:15) were synthesized and named as PEA, PEB, PEC, PED, and PEE, respectively. According to the obtained monomer reactivity ratios, the SCPs with a range from medium to high molecular weights (2.11×105 ≤ Mv ≤ 1.22 ×106 g/mol) were obtained. Then the influence of the SCPs and the other polyelectrolytes such as Zetag 7563 (a commercial grade of cationic polyelectrolyte) and poly(vinylsulfate) potassium salt (PVSK) as an anionic polyelectrolyte on the photoreduction of nitrobenzene over TiO2 under 400 nm LED irradiation was investigated. Zetag 7563 was not an appropriate polyelectrolyte to enhance the photoreduction of nitrobenzene due to its high Mv, and having high entanglement of polymer chains. By the addition of PVSK anionic polyelectrolyte, the conversion of nitrobenzene to aniline decreased; the PVSK has a probably greater tendency than nitrobenzene to be absorbed on the surface of TiO2 (PVSK reduces the adsorption of nitrobenzene on the surfaces of TiO2 due to the electrostatic interactions with TiO2). Simultaneous use of TiO2 with 0.01 g of PEB (with medium Mv and 4.4 meq/g charge density), led to an increase in the nitrobenzene photoreduction (95% conversion) in comparison with application of bare TiO2 (53% conversion). It supposes that the selection of appropriate SCPs can facilitate the access of reactants to each other and enhance the nitrobenzene photoreduction.