Synthesis of TiO2/nZVI nanocomposite for nitrate removal from aqueous solution

International Journal of Industrial Chemistry https://doi.org/10.1007/s40090-019-0186-3 RESEARCH Synthesis of TiO2/nZVI nanocomposite for nitrate removal from aqueous solution Zahra Hejri1 · Mehri Hejri1 · Maryam Omidvar1 · Sadjad Morshedi1 Received: 31 August 2018 / Accepted: 4 June 2019 © The Author(s) 2019 Abstract To develop a new adsorbent for removal of nitrate and to enhance the adsorbent separation from aqueous solution, surface modification of titanium dioxide nanoparticles with nano-zero-valent iron (nZVI) was performed through chemical coprecipitation of magnetic nanoparticles on TiO2 surface. Morphological, structural and magnetic properties of modified adsorbents (TiO2/nZVI) were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared radiation (FTIR) and vibrating sample magnetometer (VSM). To determine the ionic strength effect and optimal removal conditions, the effect of contact time (60–210 min), pH (4–10) and adsorbent dosage (0.5–1.5 g/L) on adsorption efficiency were studied, using response surface method. Obtained results showed that the nitrate removal efficiency decreased with increasing ionic strength. The T iO2/nZVI nanocomposites exhibited a ferromagnetic behavior and its saturation magnetization was 795.28 memu/g. The maximum nitrate removal (98.226%) achieved by modified T iO2 was about 14.65% higher than the unmodified nanoparticles. The optimized adsorption parameters were: adsorbent dosage 0.982 g/L, pH 4.185 and the contact time 150.091 min. Keywords Titanium dioxide · nZVI · Nitrate · Aqueous solution · Adsorption Introduction Nitrate is often found in drinking water because of human activities such as excessive utilization of chemical fertilizers, inappropriate disposal of industrial, human and animal wastes, etc. Nitrogen is converted to nitrate in the soil and since nitrate is dissolvable in water, it enters groundwater and eventually drinking water through the rain [1]. Increasing nitrate in drinking water has two adverse health effects: induction of blue-baby syndrome or methemoglobinemia, especially in infants, and the formation of carcinogenic nitrosamines [2]. * Zahra Hejri Mehri Hejri Maryam Omidvar Sadjad Morshedi 1 Department of Chemical Engineering, Quchan Branch, Islamic Azad University, Quchan 94791‑76135, Iran Conventional nitrate removal technologies including ion exchange, reverse osmosis, electrodialysis, biological and chemical denitrification, are often costly and complex with low efficiency and sub-products [2–5]. Adsorption has been proposed as an attractive technology for removal of different pollutants from water due to its process simplicity, selectivity and reusability of the adsorbent, low cost and environment-friendly nature [6–14]. Khezri et al. [15] investigated the adsorption of nitrate anions from aqueous solutions on ammonium-functionalized magnetic mesoporous silica. The removal efficiency of NO3− from solution was around 86.24% by the constructed adsorbent under the optimal experimental conditions. Nowadays, nano-adsorbents are widely used to efficiently eliminate the pollutants from water due to high surface-to-volume ratio, easy synthesis and rapid sorption [3, 16]. Bhatnagar et al. [2] have investigated the removal of nitrate from aqueous solution using alumina nanoparticles and achieved the maximum absorption capacity of 4 mg/g at 25 ± 2 °C and pH 4.4. Farasati et al. [17] eliminated nitrate from contaminated waters using anion exchanger Phragmites australis nanoparticles. The highest adsorption rate was obtained at pH 6 using 0.3 mg/L adsorbent. Zhao et al. [13] reviewed the recent 13 Vol.:(0123456789) International Journal of Industrial Chemistry works on the preparation of polymer composites and their application in the efficient removal of heavy metal ions from aqueous solutions under different conditions. Mohammadi et al. [18] synthesized carboxylated chitosan modified with ferromagnetic nanoparticles for adsorptive removal of nitrate anions from aqueous solutions. The maximum amounts of adsorption onto prepared nanoparticles were obtained in acidic conditions with 2 g/L of adsorbent. Yazdi et al. [19] removed nitrate from aqueous media by functionalized chitosan–clinoptilolite nanocomposites successfully. Recent studies have shown that zero-valent iron (Fe0), especially in nanoscale form, may potentially be used for water remediation, due to its affinity for a large number of contaminants, large specific surface area, and high surface reactivity [20–23]. Muradova et al. [20] investigated the removal of nitrate from groundwater by Fe/Cu bimetallic nanoparticles. They found that the rate of nitrate reduction increased by adding the ratio of copper particles to ZVI in two-part metal particles. Zou et al. [24] reported the excellent removal capacity of nZVI-based materials for various heavy metal ions. Sepehri et al. [25], removed nitrate (up to 84%) from aqueous solution by zero-valent iron nanoparticles reinforced with natural zeolite. Furthermore, the adsorption of some contaminants including amido black dye (up to 88% removal), ibuprofen (92%), ametryn (88%), propranolol drug residue (90%), pantoprazole drug residue (89%), secbumeton herbicide (90%), β-estradiol (82%), atrazine herbicide(95%), cyanazine (80%) onto iron nanocomposite material as adsorbent has been investigated by Ali et al. [26–34]. Titanium dioxide is a nontoxic material that has been applied in environmental treatments such as water and air disinfection because of relatively low price, corrosion resistance and its unique properties such as strong photocatalytic activity and high physical and chemical stability [35–38]. Titanium dioxide nanoparticles have been used to photocatalytic and adsorption removal of some pollutants [36, 39–48], but to the best of our knowledge, any research focused on removal of nitrate from water by adsorption on magnetized titanium dioxide nanoparticles and its comparison with unmodified TiO2 nanoparticles has not yet been reported. The main aim of this study was to investigate the nitrate removal efficiency of T iO2 nano-particles grafted with nZVI. Experimental Materials Nano-TiO2 powder (anatase-phase crystal structure with average particle size of about 25 nm) was supplied by Nanolin, Germany. Potassium nitrate (99%), ferric trichloride (FeCl3·6H2O) with 99% purity, molecular mass 270.33 g/ 13 mol and density of 1.82 g/cm3, sodium borohydride (NaBH4) with a purity of 99%, molecular weight 37.83 g/mol and density of 0.0005 g/cm3 and ethanol (≥ 99% purity) from Merck, Germany were used. Preparation of TiO2/nZVI nano‑adsorbent nZVI was synthesized in an anaerobic chamber via the reduction of Fe3+ ions with sodium borohydride as a reducing agent according to the method described by Huang [49]. Briefly, FeCl3·6H2O was dropped to NaBH4 solution in a 1:2 volume ratio. The black nZVI was s (...truncated)