Extraction of iron from laterite soil and green synthesis of laterite nano iron catalyst (GLaNICs) for its application as Fenton's catalyst in the degradation of triclosan

Personal care products (PCP) are products used for the external application on body parts includes a wide variety of cosmetics and oral hygiene materials. PCPs differ from pharmaceutical products by their nature and production process. Some of the PCPs includes underarm deodorants, deodorant soaps, and dermatological and topical preparations for protection of skin (Bhargava & Leonard 1996). Current usage of personal care products has spiked up exponentially in past 50 years. Production of these PCPs includes many natural and synthetic chemicals among which triclosan has found its part exhibiting unique biocidal characteristics. Triclosan (2,4,4′-trichloro-2′-hydroxydiphenyl ether) is a synthetic, nonionic, broad spectrum antibiotic and antimicrobial agent that has been used extensively in personal care products, including underarm deodorants, deodorant soaps, livestock productivity and dermatological and topical preparations for protection of skin (Bhargava & Leonard 1996; Pragada & Thalla 2021). The mild nature of triclosan compared to alcohol, chlorhexidine gluconate, and para-chloro-meta-xylenol and greater sustained activity makes it one of the prime materials in the manufacturing of most of the PCPs. Despite of its usage, triclosan has shown a greater degree of toxicity with lethal dosage of 19–29 mg/kg for mice and rats. Clinical pathological studies have also shown reductions in red blood cell count, hemoglobin, and hematocrit in females and clotting time was increased in males (Bhargava & Leonard 1996). PCP industry wastewater contains many contaminants which are persistent to the degradation and resistant to biotransformation and accumulate in the environment if discharged untreated (Thompson et al. 2005; Adhikari et al. 2022; Bakare & Adeyinka 2022). Collection of pharmaceutical and PCP industries are sewerage systems.

Resistance to biotransformation made triclosan unsuitable for biological treatment. Lépesová et al. (2019), identified bacterial strain such as Citrobacter freundii and Serratia spp. known for its triclosan resistance in sewage sludge rendering resistance to biotransformation (Lépesová & Krahulcová 2019). Adsorption is known to remove triclosan effectively with its limitations in the maintenance and regeneration of adsorbent. Conventional treatment process like activated sludge process yields more satisfactory results in the triclosan removal than trickling filters (Heidler & Halden 2007; Nandikes et al. 2022). However, chemical treatment like advanced oxidation process is most advanced technologies in treating organic compounds. Despite its limitations, such as low mineralization with ozonation, formation of halogenated compounds with chlorination, and high energy consumption with electro Fenton's oxidation, it is proven to be highly efficient in triclosan removal (Luo et al. 2019). Divalent catalyst iron helps in the faster dissociation of hydrogen peroxide into hydroxyl radicals acting as a catalyst in the process. Investment on catalyst for its large-scale application and disposal of huge quantity of sludge generated marks the limitation of conventional Fenton's oxidation. To overcome the cost involved in the commercial iron purchase and to make the process a more cost-effective replacement for commercial iron has been studied by various researchers. Previous studies have claimed the application of iron extracted from natural laterite soil as a Fenton's catalyst in the degradation of organic compounds (Sangami & Manu 2019; Bhaskar et al. 2021). However, heterogeneous Fenton's oxidation driving by nano iron catalyst have proven efficient in the degradation of various organic contaminants (She 2010; Chen et al. 2017; Sangami & Manu 2018; Bhaskar et al. 2020).

Laterite soil by its characteristic has 30–40% of iron which makes at naturally available iron rich mineral. The investigation on usage of laterite iron as a catalyst in its natural form, iron leached from laterite soil by chemical method, bioleached laterite iron and nanoparticles synthesised from leached laterite iron confirms its role as a catalyst in the Fenton's oxidation (Sangami & Manu 2017; Bhaskar et al. 2021). Psidium guajava, a tropical plant extensively rich in phytochemicals such as alkaloids, flavonoids and polyphenols are used for the synthesis of nanoparticles. Polyphenols present in the plant extracts are proven to actively acts as capping agent around the particles reducing its size and increasing the surface area. Properties of nanoparticles like size, shape and surface area depends on the plant extract and the precursor used in the process of synthesis. Interaction of various organic functional groups with precursor used with the Psidium gujava makes it one of the prominent plants used in the green synthesis of wide variety of nanoparticles.

Potential application of nano catalyst synthesized using natural laterite iron extract as precursor are in need to be evaluated for its efficiency, cost-effectiveness and treatment time reduction. Nanoparticles synthesis using Psidium guajava leaf extract and laterite iron as percussor for its application in Fenton's degradation of triclosan has not been studied so far. In this view, the present study encompasses synthesis of green iron nano iron catalyst using laterite iron extract as a percussor and Psidium guajava extract for its application of in the degradation of triclosan.

All the chemicals used for the synthesis of nanoparticles and triclosan removal were analytical grade reagents. Triclosan (99.5%) was procured from Sigma Aldrich. Sulphuric acid was procured from Merck India which is used to adjust the pH. Hydrochloric acid, hydrogen peroxide, sodium thiocyanate, potassium thiocyanate, titanium sulfate, 1–10 phenanthroline, ferrous ammonium sulfate, and sodium carbonate were purchased from Merck India.

The iron nanoparticles were synthesized from guava leaves. Instead of using iron salts, locally available laterite soil was used as a source of iron.

Iron laterite soil was extracted using chemical leaching method as described in Sangami & Manu (2017). One gram of laterite soil was weighed and mixed with 10 mL of concentrated HCl. The mixture was heated to dry and kept in an oven for 1 h to remove any organic matter if any. Cooled mixture at room temperature is again boiled on addition of 10 mL distilled water and 10 mL HCl for 1 min. Hot distilled water of about 20 mL was added when solution was boiling and cooled to room temperature. The solution was filtered using Whatman filter paper No. 42 and stored at 4 °C for further use. Iron content in the extracted solution was measured using UV-spectrophotometer (APHA Method 4500-F 1992).

Chemically leached laterite iron solution was used as percussor for the preparation of nano iron catalyst using Psidium guajava leaf extract. Fresh leaves of Psidium guajava was collected, washed to remove any dirt particles with distilled water and dried in an oven at 40 °C for 2 days. Dried leaves were powdered and stored for the synthesis of nano catalyst. About 5 g of powdered Psidium guajava leaves was mixed with 100 mL distilled water and heated in a hot plate at 80 °C for 60 min. Solution was cooled and filtered using Whatman filtered paper 42 and stored for further use. Laterite iron and Psidium guajava leaf extract was mixed in a proportion of 1:1, filtered and stored in a moisture free container. Synthesized nanoparticles were characterized using SEM-EDS, XRD, BET and FTIR.

Fenton's oxidation of triclosan was carried out with initial of 2 mg/L (Sangami & Manu 2016, 2018). About 0.1 g of GLaNICs was added to solution containing triclosan taken in a conical flask. The solution was adjusted to pH 3 using 1 N H₂SO₄ and allowed for 10 min to ensure proper mixing. Experimentation was conducted with different dosages of H₂O₂ (100–400 mg/L). Samples were drawn at regular intervals for analysis. During sampling, each time 1 mL of sodium thiosulphate was added to arrest the reaction (Khan et al. 2009). Concentration of triclosan was measured using HPLC Agilent 1200 with a C18 reverse phase column (pore size 3.5 μm, 100 × 0.46 cm), using water and methanol (in the ratio of 58:42) as mobile phase injected with a flow rate of 1.0 mL/min employing diode array detector (DAD) (Anupama & Shrihari 2018; Bhaskar et al. 2019). Chemical oxygen demand (COD) was measured using calorimetric method (APHA Method 4500-F 1992). pH was measured using digital pH meter. Ferric iron was measured by potassium thiocyanate method using UV-Vis spectrophotometer (Mellon 1941). H₂O₂ was measured using UV-spectrophotometer (Eisenberg 1943). All the analyses were carried out in duplicates.

BET surface areas for BLFeNPs was found to be 11.707 m²/g (Soon & Hameed 2011).

Sires et al. (2007) investigated suitability of electro-Fenton's oxidation in the degradation of both triclosan and triclocarban and identified oxalic acid, formic acid, maleic acid as degradation products with 2,4-dichlorophenol, 4-chlorocatechol and chlorohydroquinone as hydroxylated derivatives (Sir et al. 2007). Munoz et al. (2012) identified three major degradation compounds on Fenton's oxidation of triclosan and claims p-hydroquinone of triclosan forms when OH* radicals attack triclosan in para-position while 2,4-DCP and 4-CC forms when the OH* radical attacks to triclosan in the ortho-position leading to the opening of one of the aromatic rings (Munoz et al. 2012).

Iron measured during the investigation shows maximum of 31 mg/L of iron leached out of nano catalyst participated in the degradation of triclosan. Initially ferrous form of iron was observed to be more with a concentration of 19.75 mg/L at 5 min later its ferric form of iron was observed to be more by 40 min. This change in iron form is in consistent with the degradation of triclosan where maximum degradation lasts for 40 min, thereby attaining a constant rate.

Fenton's treatment of triclosan is shown to be active in acidic pH. During the Fenton's process hydrated ferrous ions get transformed into the colloidal ferric species forming the ferric hydroxyl complexes, thereby reducing efficiency at basic pH. During the study pH maintained was varied slightly from 3.0 to 4.4 which favoured the oxidation process forming hydroxyl radicals (Kang & Hwang 2000; Burbano et al. 2005).

Laterite-based nano iron catalyst was successfully synthesized with extracted laterite iron as precursor using Psidium guajava plant extract by green synthesis. Synthesized nano iron catalyst was confirmed and evaluated for its application as a Fenton's catalyst in the degradation of triclosan. At acidic pH, triclosan is shown to be amenable for degradation with synthesized nano catalyst on Fenton's oxidation. Maximum degradation of 69.5% was observed at pH 3 with 0.1 g/L of catalyst and 200 mg/L of H₂O₂ at 1:2 ratio and corresponding COD removal observed was 54.4% within 120 min of treatment. Degradation of triclosan was observed to increase with increase in hydrogen peroxide dosage. Role of hydroxyl radicals in the degradation was evaluated by measuring hydrogen peroxide concentration and reported. Both classical Fenton's oxidation and GLaNIC-driven Fenton's oxidation are found to be effective for the oxidative degradation of triclosan. Reusability studies show that synthesized iron nano catalysts can be used for three more consecutive cycles. The study claims the use of natural laterite iron-based nanoparticles as a catalyst in Fenton's degradation of triclosan promising cost-effective treatment.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.