INTRODUCTION:

The water pollution caused by heavy metal ions has been increasing the social concerns that are derived from improper handling and managing different types of hazardous wastes in the environment. [1]

Heavy metals like Chromium, Cadmium, Zinc, Mercury, Lead, Copper, Arsenic etc., enter into the environment through industrial waste water, municipal sewage, acid mine drainage and other sources. Chromium (VI) is frequent contaminant in the waste water coming from industrial processes such as electroplating, pigment production, leather tanning, textile dying etc [3]. Chromium exist mainly in two major oxidation states i.e., hexavalent Chromium and trivalent Chromium. The Cr (VI) is 100 times more toxic than trivalent form i.e., Cr (III) [2]. According to WHO standards and BIS, permissible limit of Chromium in drinking water is 0.05mg/l [2]. The hexavalent Cr (VI) species are very harmful it can cause irritation to the nose, such as runny nose, nosebleeds, and ulcers and holes in the nasal septum. Cadmium exist in environment as earth oxidation state i.e. Cd (0) and Cd (II). Various studies shows that oxidation state of Cadmium (II) is 100 times toxic then the Cadmium (0). According to WHO standards, permissible limit of cadmium in potable water is 0.005mg/l. If it crosses this accessible limit, may cause human carcinogen and teratogen severally impacting lungs, kidneys, liver and reproductive organs. Photo catalytic reduction technology is relatively new technique for the removal of heavy metal in waste water [4]. Nanotechnology method is widely used because it holds out a promise of immense improvements in manufacturing Technologies [5]. Nanomaterials are efficient, cost effective and environmental friendly, durability at high temperature, large surface area, high reactivity, high specificity, and ability to penetrate through porous media to remove the contaminants selectively and is an alternative to existing treatment materials.[6]. Semiconductor photo catalysis are newly developed applications and can be applied to degrade heavy metals conveniently. Recently there are many research works related to the use of semiconducting materials such as Titanium dioxide (TiO₂), Zinc oxide (ZnO), Tungsten oxide (WO₃), Strontium titanate (SoTio₂), Hematite (Fe₂O₃) as photo catalysis for various applications [7]. Iron oxide (Fe₂O₃) one of the most commonly used semiconductors in photo catalytic process and is characterized by its high surface area, non toxicity, low cost, high-efficiency, low energy band gap etc. The basic mechanism that takes place in photo catalytic reaction is the production of electron hole couple. When a photo catalyst illuminated by the light stronger than its band gap energy, electron hole pair diffuses out of photo catalyst [8]. Reusability of iron oxide based nanomaterial leads to a decrease in the economic burden.[9] The application of experimental design methodologies in the photo catalytic processes can improve the remediation efficiency and with lesser number of experiments. The most relevant multivariate techniques used in analytical optimization is the response surface method (RSM) with a central composite design (CCD) [9] To optimize the process variables for the reduction process the combined effect of initial metal ion concentration, catalyst dosage and pH, a central composite design in response surface methodology using design expert software version 7.0.0 (stat-lase) is used. The best operating conditions are estimated and then validated with confirmatory experiments.

The regeneration studies are performed making it more commercially viable as once separated, this catalyst can be reused because of its regenerative property under photo catalytic reaction. The ability of the photo catalyst to be reused is an essential practical aspect of the cost effectiveness in every related process [10].

MATERIAL AND METHODS:

Alkali used for regeneration studies of ironoxide nanoparticles was NaOH. It was chosen as a basic media for alkali wash. Iron oxide nanoparticles washed with 0.01N NaOH and desiccated at 100 degree Celsius.

HCl of 0.1N for acid wash was used.

Instrumentation:

The proposed work was carried out on a Shimadzu UV-visible spectrophotometer (model UV-1800 series), which possesses a double beam double detector configuration with a1 cm quartz matched cell. All weighing was done on electronic balance (Sansui-vibra DJ-150S-S). Photocatalytic Reactor with a 125 watt bulb was used.

Experimental Procedure:

In heavy metal removal processes, desorption/ regeneration of absorbents is one of the essential aspects as it controls the economy of water treatment technology [11]. For effective regeneration of absorbents and metal recovery, acids (such as HCl, H₂SO₄, HNO₃, HCOOH and CH₃COOH), alkalis (such as NaOH, NaHCO₃, Na₂CO₃, KOH, K₂CO₃), salts (such as NaCl, KCl, (NH₄)₂SO₄, CaCl₂. 2H₂O, NH₄NO₃, KNO₃ and C₆H₅Na₃O₇.2H₂O), deionized water, chelating agents and buffer solutions (such as bicarbonate, phosphate and tris) were used in various studies [12].

Desorption of metal ions in acidic media appeared to be rapid and higher than neutral media. The possible mechanisms and conditions of desorption by acids are as follows Low pH favors desorption and /or dissolution of metal cations. Strong competition between H+ ions and metal cations for adsorption sites causes displacements of cations into acid solution. Acidic condition favors dissolutions of Fe and Al oxide/silicate adsorption surfaces and thus the release of adsorbed/surface-precipitation metals. Acid reacts with residual alkalinity and lowers adsorption capacity.

Various salts such as NaCl, KCl, (NH₄)₂SO₄, CaCl₂.2H₂O, NH₄NO₃, KNO₃ and C₆H₅Na₃O₇.2H₂O were used for desorption. EDTA was found to be one of the most effective desorbing agents in many studies [13].

In order to use Fe₂O₃ for industrial scale it is necessary to make them attractive with regard to the usual methods of clean up. Regeneration of loaded catalyst is a key factor in improving the economy of photo catalytic process. The reusability of photo catalyst is noted to set up the constancy while studying reclaimed photo catalyst every parameters together with the irradiation time, concentration, amount of photo catalyst were kept constant. The photo catalyst was removed from the solution mixture through centrifuge. The photo catalyst was washed again with deionised water, desiccated at 100 degree Celsius in the oven. Various alkali can also be used for regeneration studies of heavy metals. Commonly used alkalis for recovery of heavy metals are NaOH, Na₂CO₃, KOH and K₂CO₃. NaOH was chosen as a basic media for alkali wash. Various acids such as HCl, H₂SO₄, HCOOH and CH₃COOH are used as acid wash media. In this study, HCl of 0.1N for acid wash was used and it was found more effective than NaOH and deionised water.

The reusability of photo catalyst is noted in direct to set up the constancy while studying reclaimed photo catalyst every parameter together with the irradiation time, concentration, amount of photo catalyst were kept constant.

Best five results obtained in the experiments carried out while optimizing variable parameters using Response surface methodology were taken for regeneration study.Combination of 2ppm,4pH,150mg gave 92.27% Reduction:10ppm,4pH,150mg gave 81.25% Reduction: 2ppm, 4pH, 50mg gave 61.96% reduction:6ppm, 4pH, 100mg gave 59.42% reduction: 6ppm,7pH,150mg gave 59.25% reduction These values were obtained for reduction of Chromium (VI) and were taken for regeneration study.Similarly for Cadmium (II) reduction following best five results were taken for regeneration studies. 2ppm, 4pH, 150mg gave 94.43% reduction: 2ppm, 10pH, 150mg gave 75.52% reduction: 2ppm, 7pH, 100mg gave 67.92% reduction: 6ppm, 7pH, 150mg gave 65.02% reduction: 10ppm, 7pH, 100mg gave 58.65% reduction were taken for regeneration study. The photo catalyst was removed from the solution mixture through centrifuge (4000 rpm) and it was washed with deionised water and desiccated at 100 degree Celsius in the oven. Alkali was also used for regeneration studies of ironoxide nanoparticles. NaOH was chosen as a basic media for alkali wash. Iron oxide nanoparticles washed with 0.01N NaOH and desiccated at 100 degree Celsius. HCl of 0.1N for acid wash was used. Washed nanoparticles were charged into the fresh stock solution of known concentration. After 150min, 1ml of sample was collected and the collected samples centrifuged using micro centrifuge and solution was taken for U.V analysis to know the absorbance. This was repeated for five times for a individual sample of known concentration of Chromium (VI) and Cadmium (II) solutions.

RESULTS AND DISCUSSION:

Fig. 1: Reusability of α-Fe₂O₃ in reduction of Chromium (VI) v/s Number of cycles

The regeneration studies were carried on the Iron oxide nanoparticles by washing with Deionised water, Alkali 0.01N NaOH and 0.1 N HCl and it was found that there was a little decrease in the percentage reduction of Chromium (VI) after every cycle for each sample Fig1. This was due to loss of some nanoparticles at the time of washing, drying and reusing repeatedly.

Fig. 2: Reusability of α-Fe₂O₃ in reduction of Cadmium (II) v/s Number of cycles

The regeneration and reusable experiments were performed for Cadmium Fig 2. It was observed that the prepared α-Fe₂O₃ was stable and regenerable using strong acid (HCl) as desorbing agent. The regeneration studies were carried on the Iron oxide nanoparticles by washing with Deionised water, Alkali 0.01N NaOH and 0.1 N HCl and it was found that there was a little decrease in the percentage reduction of Cadmium (II) after every cycle for each sample. This was due to loss of some nanoparticles at the time of washing, drying and reusing repeatedly which was even observed in the study of Chromium (VI) reduction. It was observed that the prepared α-Fe₂O₃ was stable and regenerable.

CONCLUSION:

The iron oxide nanoparticles prepared by Sol-Gel method was haematite.

Combination of 2ppm, 4pH, 150mg gave 92.27% Reduction: 10ppm, 4pH, 150mg gave 81.25% Reduction: 2ppm, 4pH, 50mg gave 61.96% reduction: 6ppm, 4pH, 100mg gave 59.42% reduction: 6ppm, 7pH, 150mg gave 59.25% reduction These values were obtained for reduction of Chromium (VI) and were taken for regeneration study.

Similarly for Cadmium (II) reduction following best five results was taken for regeneration studies. 2ppm, 4pH,150mg gave 94.43% reduction: 2ppm,10pH,150mg gave 75.52% reduction: 2ppm, 7pH, 100mg gave 67.92% reduction: 6ppm,7pH,150mg gave 65.02% reduction: 10ppm, 7pH, 100mg gave 58.65% reduction were taken for regeneration study. The regeneration and reusable experiments were also performed for both Chromium and Cadmium. It was observed that the prepared α-Fe₂O₃ was stable and regenerable using strong acid (HCl) as desorbing agent. α-Fe₂O₃ nanoparticle dose was the most significant factor affecting Cr (VI) and Cd (II) removal.

α-Fe₂O₃ could be reused without significant losses of their initial properties. It was found that there was a little decrease in the percentage reduction of Cadmium (II) after every cycle for each sample. This was due to loss of some nanoparticles at the time of washing, drying and reusing repeatedly which was even observed in the study of Chromium (VI) reduction.

ACKNOWLEDGEMENT:

The authors are grateful to the authorities of SDMCET Dharwad, KLEIT Hubli and REC Hulkoti

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

REFERENCES:

1. Hu, Jin‐Song, et al. "Synthesis of hierarchically structured metal oxides and their application in heavy metal ion removal." Advanced Materials 20.15 (2008): 2977-2982.

2. Kakavandi, Babak, et al. "Enhanced chromium (VI) removal using activated carbon modified by zero valent iron and silver bimetallic nanoparticles." Journal of Environmental Health Science and Engineering 12.1 (2014): 115.

3. Park, Hyunwoong, et al. "Surface modification of TiO2 photocatalyst for environmental applications." Journal of Photochemistry and Photobiology C: Photochemistry Reviews 15 (2013): 1-20.

4. Tayeb, Aghareed M., and Dina S. Hussein. "Synthesis of TiO2 nanoparticles and their photocatalytic activity for methylene blue." American Journal of Nanomaterials 3.2 (2015): 57-63.

5. Khan, S. H., B. Pathak, and M. H. Fulekar. "Spherical Surfaced Magnetic (Fe3O4)‎ Nanoparticles as Nano Adsorbent Material‎ for Treatment of Industrial Dye Effluents‎." International Journal of Nanoscience and Nanotechnology13.2 (2017): 169-175.

6. Hussein, F. M., S. S. Al-Saleh, and S. M. Aliwi. "Photoreduction of Cd+ 2 in aqueous TiO2 suspention." Iraqi National Journal of Chemistry 24 (2006): 587-595

7. Athapaththu, Samindika. "A Comprehensive Study of Cd (II) Removal from Aqueous Solution via Adsorption and Solar Photocatalysis." (2013)

8. Dave, Pragnesh N., and Lakhan V. Chopda. "Application of iron oxide nanomaterials for the removal of heavy metals." Journal of Nanotechnology 2014 (2014).

9. Esfahani, A. Ramazanpour, et al. "Pb (II) removal from aqueous solution by polyacrylic acid stabilized zero-valent iron nanoparticles: process optimization using response surface methodology." Research on Chemical Intermediates40.1 (2014): 431-445.

10. Sharafi, Kiomars, et al. "Apllication of response surface methodlogy (RSM) for statistical analaysis, modeling and optimization of removal of phenol from aqueous solutions by aluminum- modified scoria powder." Int Res J Appl Basic Sci9.10 (2015): 1789-98.

11. Gowda, M. S., P. Shiva K. Kumar, and R. M. Kulkarni. "Photo catalytic deprivation to methylene blue via ZnO nano particles by advanced oxidation process." Int. Res. J.

Received on 06.06.2020 Modified on 01.07.2020

Asian J. Research Chem. 2020; 13(5):319-322.

DOI: 10.5958/0974-4150.2020.00061.9