A review of recent advances in visible light initiating systems using free radical, cationic and hybrid photoinitiators is presented.

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In this study, we prepared polyethyleneimine (PEI) and graphene oxide (GO) composite adsorbent PEI-GO through an amidation reaction between the amine groups of the PEI and the carboxyl groups of the GO. Adsorption performance of the PEI-GO was tested by removing Cr(VI) ions from an aqueous solution. The physico-chemical properties of the GO, pristine and Cr(VI) ions loaded PEI-GO were investigated by the FT-IR, SEM-EDX and XPS methods. To investigate the adsorption kinetics of Cr(VI) ions onto this newly developed PEI-GO, we performed a batch of experiments under different adsorption conditions: content of the PEI in the PEI-GO, solution pH, initial Cr(VI) ion concentration, adsorption temperature and contact time. The prepared PEI-GO exhibited an encouraging uptake capacity of 539.53 mg/g. The adsorption process was fast, within the first 1 h, Cr(VI) ion adsorption onto the PEI-GO was about 71 %, and the adsorption equilibrium could be obtained within 14 h. Kinetics experiments indicated that the adsorption process could TP * P T 2 be described by the pseudo-second-order kinetic model. Furthermore, our adsorption equilibrium data fit the Langmuir isotherms well (R 2 >0.99). The removal mechanism of Cr(VI) ions from the solution consists of two steps: (1) Cr(VI) ions binds to the 4PEI-GO by the electrostatic interaction between the negatively charged Cr(VI) ions species and the protonated amine groups of the 4PEI-GO; and (2) small part of Cr(VI) ions were reduced to Cr(III) ions with the assistance of π electrons on the carbocyclic six-membered ring of the 4PEI-GO and then bind on the 4PEI-GO by the electrostatic attraction between Cr(III) ions and negatively charged groups (COO − ) of the 4PEI-GO. Based on the results obtained in this work, it can be concluded that the prepared PEI-GO can be an effective and potential adsorbent for removing Cr(VI) ions from an aqueous solution.

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