Application of superparamagnetic iron oxide nanoparticles (SPIONs) for heavy metal adsorption: A 10-year meta-analysis

Water contamination with heavy metals has become a major concern in the present time, which necessitates the need for effective and flexible techniques for water remediation. During the last few years, superparamagnetic iron oxide nanoparticles (SPIONs) based adsorbents and their composites have gathered significant attention in their adsorption potential towards the heavy metal ions in an aqueous medium. In the present systematic review and meta-analysis, the adsorption performance of nano adsorbents based on SPIONs for heavy metals (lead, mercury, chromium, copper, arsenic, nickel, and cadmium) has been compiled from the year 2011 to 2020. A total of 232 articles were assessed to be suitable for the review section after a thorough screening and analysis. In addition, 180 published studies were entitled to meet the quantifiable criteria for the meta-analysis. Computer programming languages were employed to do the correlation analysis, heterogeneity analysis and to construct the Forest plot. Further subgroup analysis was done for each heavy metal ion to know the cause of variance in the data. According to the collective data, the adsorption capacity ranged from 0.23 and 1476.4 mg/g. The systematic review of the studies revealed that the metal ion removal efficiency of the SPIONs varied between 50 and 100%, while the pH range of 4–7 was the most widely investigated range in the elimination of heavy metal ions. From the analysis of the studies, the adsorption experiments were carried out in the period between 1 and 2500 min. The present article aims to highlight the need to achieve maximum metal ions removal efficiency in the water treatment process and study the relationship of adsorption dosage on removal efficiency. A panel of published data (k = 258) exhibited that the I² in terms of pooled removal efficiency data was 79%.The statistical findings concluded that no publication bias existed.