Synthesis, characterisation and methyl orange adsorption capacity of ferric oxide\u2013biochar nano-composites derived from pulp and paper sludge

Nhamo Chaukura,Edna C Murimba,Willis Gwenzi

doi:10.1007/s13201-016-0392-5

Abstract

A Fe2O3–biochar nano-composite (Fe2O3–BC) was prepared from FeCl3-impregnated pulp and paper sludge (PPS) by pyrolysis at 750 °C. The characteristics and methyl orange (MO) adsorption capacity of Fe2O3–BC were compared to that of unactivated biochar (BC). X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the composite material was nano-sized. Fourier transform infrared (FTIR) spectroscopy revealed the presence of hydroxyl and aromatic groups on BC and on Fe2O3–BC, but Brunauer–Emmett–Teller (BET) surface area and Barrett–Joyner–Halenda (BJH) porosity were lower for Fe2O3–BC than BC. Despite the lower BET surface area and porosity of Fe2O3–BC, its MO adsorption capacity was 52.79 % higher than that of BC. The equilibrium adsorption data were best represented by the Freundlich model with a maximum adsorption capacity of 20.53 mg g−1 at pH 8 and 30 min contact time. MO adsorption obeyed pseudo-second-order kinetics for both BC and Fe2O3–BC with R2 values of 0.996 and 0.999, respectively. Higher MO adsorption capacity for Fe2O3–BC was attributed to the hybrid nature of the nano-composites; adsorption occurred on both biochar matrix and Fe2O3 nanocrystals. Gibbs free energy calculations confirmed the adsorption is energetically favourable and spontaneous with a high preference for adsorption on both adsorbents. The nano-composite can be used for the efficient removal of MO (>97 %) from contaminated wastewater.

Highlights

Dyes are widely used in textile, plastic, paper, food, and cosmetic industries
The increased pH for BC can be attributed to the removal of volatiles in the biochar matrix during pyrolysis, which increased the pH of the biomass from 7.31 to 8.46 for BC, while acidic pH of Fe2O3–BC could be due to impregnating the biomass with FeCl3 prior to pyrolysis
This study indicates that the biochar and Fe2O3–biochar nano-composites prepared from paper pulp sludge can be used as an adsorbent for the treatment of wastewater containing methyl orange (MO)

Summary

Introduction

Dyed wastewater from industrial processes pose public and environmental risks such as aesthetic pollution due to their colour (Pathania et al 2013), and breakdown to release potentially toxic, carcinogenic or mutagenic products such as benzidine, naphthalene and other aromatic compounds (Bhatt et al 2012; Belaid et al 2013; Haldorai and Shim 2014; Mittal and Mishra 2014). Discharge of dyed wastewater into aquatic systems reduces light penetration and the photosynthetic activity of aquatic plants (Subasioglu and Bilkay 2009: Said et al 2013). Such polluted water can be a breeding ground for bacteria, viruses and vectors causing water-borne diseases. Acute exposure can cause increased heart rate, vomiting, shock, cyanosis, jaundice, quadriplegia, and tissue necrosis in humans (Azami et al 2012; Gong et al 2013)

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