RESEARCH ARTICLE Photodegradation of 4-nitrophenol over B-doped TiO 2 nanostructure: effect of dopant concentration, kinetics, and mechanism Vandana Yadav 1 & Priyanka Verma 1 & Himani Sharma 2 & Sudhiranjan Tripathy 3 & Vipin Kumar Saini 1 Received: 8 May 2019 /Accepted: 1 October 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract The 4-nitrophenol (4-NP) is one of the carcinogenic pollutants listed by US EPA and has been detected in industrial wastewater. This study investigates the photocatalytic degradation of 4-NP with TiO 2 and boron (B)-doped TiO 2 nanostructures. The degradation on undoped and B-doped TiO 2 with various boron loadings (1–7%) was studied to establish a relationship between structure, interface, and photo-catalytic properties. The results of XRD, micro Raman, FTIR, and HRTEM show that the B doping has improved the crystallinity and induces rutile phase along with anatase (major phase). The N 2 adsorption-desorption, SEM-EDX, and XPS indicated that the B induced the formation of mesoporous nanostructures in TiO 2 and occupies interstitial sites by forming Ti-O-B type linkage. The surface area of pure TiO 2 was decreased from 235.4 to 63.3 m 2 /g in B-TiO 2 . The photo-physical properties were characterized by UV-Vis DRS, which showed decrease in the optical band-gap of pure TiO 2 (2.98 eV) to B-TiO 2 (2.95 eV). The degradation results demonstrated that the B doping improved the photocatalytic activity of TiO 2 ; however, this improvement depends on the B concentration in doped TiO 2 . B-doped TiO 2 (> 5% B) showed 90 % degradation of 4-NP, whereas the undoped TiO 2 can degrade only 79 % of 4-NP. The degradation followed pseudo-first-order kinetics with rate constant values of 0.006 min -1 and 0.0322 min -1 for pure TiO 2 and B-TiO 2 respectively. The existence of a reduced form of Ti 3+ on the surface of TiO 2 (as evidence from XPS) was found responsible for enhancement in photocatalytic activity. Keywords Photo-catalysis . Kinetics . Mechanism . 4-Nitrophenol . Degradation pathway . TiO2 nanostructure . Doping Introduction In the current perspective, the heterogeneous photocatalysis has been considered as one of the economic, energy-efficient, and clean technology for removal of organic compounds such as amoxicillin, tetrodotoxin, ketamine, gentamicin, carbophenothion, ofloxacin, erythromycin, enrofloxacin, lido- caine, and ciprofloxacin from wastewater (Fakhri and Khakpour 2015; Fakhri and Naji 2017, 2016; Mohammadi et al. 2016; Fakhri and Kahi 2017; Fakhri et al. 2015, 2016; Fakhri and Behrouz 2015a, b; Hassani et al. 2018a, b, 2016). Heterogeneous photocatalysis utilizing titanium oxide (TiO 2 ) semiconductor as a photocatalyst is more efficient environ- mental cleanup technique in comparison to conventional tech- niques. In this process, there is no residue after degradation of contaminant or pollutant, as it slowly breaks down the large contaminant molecules. Therefore, the process of sludge dis- posal to landfill is not anymore required. Photocatalysis is also suitable for decomposition of organic and inorganic com- pounds at very low concentrations ranging from 0.01 to 10 mg/L. The catalyst used in the photocatalytic process can be reused because it does not consume and remains un- changed (Hassani et al. 2018a, b, Byrne et al. 2018). Responsible Editor: Suresh Pillai Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11356-019-06674-x) contains supplementary material, which is available to authorized users. * Vipin Kumar Saini vksaini.senr@doonuniversity.ac.in 1 School of Environment & Natural Resources, Doon University, Dehradun, Uttarakhand 248001, India 2 Department of Physics, Doon University, Dehradun, Uttarakhand 248001, India 3 Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis, #08-03, Singapore 138634, Singapore Environmental Science and Pollution Research https://doi.org/10.1007/s11356-019-06674-x