Hard-Soft PARAFAC to Study Catalytic Reduction of mixture of Nitrophenols

PARAFAC is one of several decomposition methods for multi-way data. The popularity of this model in chemistry is due to its uniqueness properties [1]. The uniqueness of PARAFAC does not hold in cases with rank overlap, rank overlap can be simply found where components have similar spectral profiles or analytes appearing in identical proportions throughout an experiment. Although constraints such as non-negativity, unimodality and, hard modeling can still make PARAFAC model useful in this regard. The hard constraint forces some or all of the concentration profiles to fulfill an equilibrium model that is refined at each iteration cycle of PARAFAC optimization process. PARAFAC with hard constraint is called Hard-Soft PARAFAC [2]. Nitrophenol-type compounds are widely applied in industries such as chemistry, petrochemical, and pharmacy and are one of the most important raw materials for synthetic medicine, dye, herbicides, insecticides, resins, and explosives. Because nitrophenol-type compounds are cancer causing and highly poisonous, it is very important to test and analyze these compounds to avoid the harm and danger they may cause to humans. Simultaneous determination of nitrophenol-type compounds is very difficult because the similarity in their structures produces overlapping signals. In recent years, the reduction of 4-nitrophenol (Nip) to 4-aminophenol (Amp) by borohydride (BH4 -) in aqueous solution has become such a model reaction that meets all criteria of a model reaction. It can be monitored easily with high precision by UV−vis spectroscopy. This is due to the fact that Nip has a strong absorption at 400 nm and the decay of this peak can be measured precisely as the function of time. Moreover, the reaction rate is small enough so that the conversion can be conveniently monitored over several minutes [3,4]. In this study, kinetic reaction of mixture of ortho, meta, and para-nitrophenol in the presence of excess BH4 - has been investigated. The Uv-vis spectra were collected during the kinetic process in 15 samples. There are three first order reactions and PARAFAC does not have unique solution because of rank deficiency in concentration profiles. Use of HSPARAFAC leads to unique solution, therefore rate constants and concentration profiles can be calculated simultaneously. In our case, computed rate constants for meta, ortho and para-nitrophenol reaction are 0.0102, 0.0100, and 0.3830, respectively.