Preparation of modified oligochitosan and evaluation of its scale inhibition and fluorescence properties

Abstract

To obtain an environmentally friendly and efficient scale inhibitor, carboxymethyl quaternary ammonium oligochitosan (CM-QAOC) was prepared from chitosan, which was depolymerized by nitrous acid, and then reacted with chloroacetic acid and glycidyl trimethyl ammonium chloride via carboxymethylation and quaternization, respectively. The chitosan derivatives were characterized by Fourier transform infrared and NMR spectroscopy. The inhibition performance for CM-QAOC was evaluated by a conductivity method and a static antiscaling test. The experiments demonstrated that CM-QAOC showed an excellent scale-inhibition performance. With a Ca2+ concentration of 240 mg/L, CM-QAOC at a concentration of 50 mg/L and pH 8.0 gave an antiscaling ratio of more than 98%. So, CM-QAOC could be applied as an excellent antiscaling agent. Furthermore, a detectable fluorescence of CM-QAOC solution was observed. To understand this interesting fluorescence phenomenon and to explore the probability of its being a fluorescent tracer, the relations between the fluorescence intensities and CM-QAOC concentrations and the pH influence on the fluorescence intensities were investigated. The results show the fluorescence intensities accorded well with the concentrations of CM-QAOC with a detection limit of 0.6046 mg/L, and the fluorescence intensity was constant within pH 5-9; this indicated that it had the potential of its being a fluorescent tracer. Thus, CM-QAOC could be applied as an antiscaling water-treatment chemical and as a fluorescence tracer directly without any further modifications. It could be self-traced online and in real time with its own fluorescence, although more work should be done to investigate its fluorescent mechanism and its tracing properties in detail.