Easily modified barium phosphate composites for effective removal of methyl blue from solution

Abstract

In this work, barium phosphate composites were easily modified by changing the reactants and surfactants to be barium sodium phosphate (NaBaPO4), barium phosphate (Ba3(PO4)2), barium hydroxyl phosphate (Ba5(PO4)3OH), and barium hydrogen phosphate (BaHPO4) (denoted NBP, BP, BPO, and BHP, respectively) using a one-step hydrothermal method. Positively charged cetyl trimethyl ammonium bromide (CTAB) on phosphate composites can slightly increase their removal capacities for methyl blue (MB) though it had no obvious effects on the composition and crystal type of materials. Dye removal experiments were carried out in a batch system to optimize operation variables such as solution pH, temperature, adsorbent dosage, contact time, and initial dye concentration. The kinetic behavior of all the materials agreed well with the pseudo-second-order model. The isothermal data of NBP and BPO fitted to the Langmuir model while Freundlich model was better to describe the isothermal data of BP and BHP. The removal capability for MB solution followed an order of NBP (249.6 ± 6.0 mg/g) > BP (226.0 ± 6.0 mg/g) > BPO (162.5 ± 5.0 mg/g) > BHP (85.84 ± 4.0 mg/g). NBP is most suitable for MB removal because of its high alkalinity: (1) The obvious increase of pH from 6.03 ± 0.10 to 12.26 ± 0.20 after adding NBP in solution can lead to improved decolorization of MB solution. (2) Strong Lewis acid base interaction between cations (Ba2+/Na+) in NBP and –SO3- in MB as well as the hydrogen bonding between PO43- in NBP and N–H or C–H in MB contributed to the high removal capacity of NBP.