RESEARCH ARTICLE Promoting sun light-induced photocatalytic degradation of toxic phenols by efficient and stable double metal cyanide nanocubes Manviri Rani 1 & Uma Shanker 1 Received: 10 February 2018 /Accepted: 1 May 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Aromatic substituted phenols and their by-products discharged from numerous industries are of environmental concern due to their toxic, carcinogenic, recalcitrant, and bioaccumulating properties. Therefore, their complete removal from waters by low- cost, efficient, environmentally friendly nanomaterial-based treatment techniques is desirable. Double metal cyanide complexes (DMCC) are the extremely useful heterogeneous and recoverable catalyst. Hence, green route has been developed for several DMCC and their photocatalytic efficiency was evaluated for degradation of toxic phenols. Herein, nanocubes for hexacyanocobaltate of iron (FeHCC ~ 200 nm), nickel (NiHCC < 10 nm), and zinc (ZnHCC ~ 500 nm) were synthesized after employing Aegle marmelos. Subsequently, at neutral pH and sunlight irradiation, 15 mg of catalysts were able to degrade the maximum extent of phenols (1 × 10 -4 M) in the order: 3-aminophenol (96% ZnHCC > 94% FeHCC > 93% NiHCC) > phenol (94% ZnHCC > 92% FeHCC > 91% NiHCC) > 2,4-DNP (92% ZnHCC > 91% FeHCC > 90% NiHCC). This is attributed to highest basicity of 3-aminophenol containing excess of free electrons. Highest catalytic potential of ZnHCC (X m = 0.54–0.43 mg/ g) is because of its highest surface area and negative zeta potential along with sharp morphology and crystallinity. Adsorption of phenols over catalyst was statistically significant with Langmuir isotherms (R 2 ≥ 0.96; p value ≤ 0.05). Small and non-toxic by- products like oxalic acid, benzoquinone, (Z)-hex-3-enedioic acid, (Z)-but-2-enal, and (Z)-4-oxobut-2-enoic acid were identified in GC-MS. Degradation modes involving hydroxylation, oxidative skeletal rearrangement, and ring opening clearly supported enhanced oxidation of phenols by • OH. Overall, due to greater active sites, high surface activity, low band gap, and semicon- ducting nature, DMCC revealed promising potential for solar photocatalytic remediation of wastewater. Keywords Double metal cyanide nanocubes . Aegle marmelos . Water . Phenols . Removal Introduction Phenols and its substituted derivatives are major organic con- stituents ordinarily found in effluents or waste released from oil refining, petrochemicals, pharmaceuticals, resin manufacturing, plastics, paint, and pulp and paper industries. They are being introduced into aquatic ecosystems and ad- versely affect the biota and ultimately humans at the exposure of 9–25 mg/L (El-Ashtoukhy et al. 2013; Jadhav and Vanjara 2004). At very low level (5 mg/L), chlorinated phenols pro- duced distinctive aroma. Therefore, the maximum tolerated amount of phenol in drinking water is set to be 1 mg/L (Saravanan et al. 2008). The physiochemical properties of phenols are presented in Table 1. Phenols are of concern be- cause of their frequent occurrence (range 1–100 mg/L), toxic- ity, carcinogenic, recalcitrant, and bioaccumulating properties (Annachatre and Gheewala 1996; Busca et al. 2008; Moussavi et al. 2008; Varma and Gaikwad 2008; Said et al. 2013; Pradeep et al. 2014). Consequently, US Environmental Protection Agency (EPA) has labeled them as specific priority pollutants (Singh et al. 2013; Babich and Davis 1981). An idea about accidental spillages, toxicity, and poisoning caused by phenols can be forwarded by Table 2. The irregular use and release of toxic and omnipresent phenols along with their metabolites in the environment (Gupta et al. 2011, 2012a, b, c; Rani 2012; Rani et al. 2017a, b) caused the necessity to Responsible editor: Suresh Pillai Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11356-018-2214-9) contains supplementary material, which is available to authorized users. * Uma Shanker shankeru@nitj.ac.in; umaorganic29@gmail.com 1 Department of Chemistry, Dr. B R Ambedkar National Institute of Technology, Jalandhar, Punjab 144011, India Environmental Science and Pollution Research https://doi.org/10.1007/s11356-018-2214-9