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• Provide correct relative order of acidity among the hydroxyl groups in oxyluciferin. • Propose the mechanism of determining major emissive species. • Explain blue-shift of emission spectra based on existence of dominant dianion in basic pH. • Explain the dependence of the emission colors on the excitation energy. The magnitude of the acidity of the oxyluciferin in water in the ground and excited state is investigated, and it is found for the first time using computational approach that the enol group of the phenol-enol species is the most acidic in the ground state, but the deprotonation of the phenol of the phenol-keto form is the most favored in the excited state. The relative order of the acidity among the hydroxyl groups in the oxyluciferin is attributed to the sequence of the O H bond lengths in the enol and phenol group of the phenol-enol form, and the phenol group of the phenol-keto species. The mechanism of determining the dominant emissive species in the excited state is proposed, and the dependence of emission light colors on the photoexcitation energy is elucidated by the high relative concentration of six chemical forms in the ground state and the absorption efficiency. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crystallized hydroxides on Al surface passive film decrease Al-PMS activity. • F− ions and organics inhibit the hydration of Al passive oxide film. • Cl− ions have a negative influence on Al-PMS reaction activity. • Acid washing can effectively remove Al surface passive oxide film. Al-peroxymonosulfate (PMS) system is an efficient way for removal of pollutants in aqueous solution. Al surface passive oxide film is a barrier to impede the electron transfer from inner metal Al to outside, whose compositions and phase structures are changed in different environment such as moisture or after recycling. In this work, for the first time, the effect of Al surface oxide structures on oxidability of Al-PMS system and its efficiency for removal of organic pollutant was investigated. It was found that if the passive oxide film on Al particles is hydrated and becomes hydroxides, the efficiency of Al-PMS system for degradation of bisphenol A (BPA) in aqueous solution decreases considerably, because the solubility of crystallized Al hydroxides is at least three orders of magnitude lower than that of amorphous Al oxides on pristine Al particles. Furthermore, the trace species in water have an influence on the hydration and structures of Al surface oxide film. For example, organics and F− ions in water will form complexes on Al particle surfaces and inhibit the hydration process, while Cl− ions corrode Al surface oxides and do not inhibit the hydration, based on the analyses of Al3+ ion concentration in their solution after BPA removal. It was also found that acid washing can remove the hydrated oxide film on Al surfaces and recover Al activity. [ABSTRACT FROM AUTHOR]

• Al was modified by soaking Al powder in water and then heat-treating in vacuum. • Modified Al has a high rate in reduction of Cr(VI) to Cr(III) ions in solution. • Modified Al exhibited an excellent recyclability in removing Cr(VI). • XPS indicated that Al surface passive oxide films become thin after modification. Zero-valent aluminum has attracted considerable attention in degradation of organic contaminants and reduction of heavy metal ions due to its very low redox potential (E 0 (Al3+/Al0) = −1.662 V). Usually there is a passive oxide film on Al surface, inhibiting its electron transfer and leading to low reaction efficiency. In this work, metal Al surface was modified by loose fine Al 2 O 3 (SM-Al) using a procedure of soaking Al powder in water for a time period and then heat-treating in vacuum. It was found that surface modification remarkably enhanced the reaction efficiency of zero-valent Al in reduction of Cr(VI) to Cr(III) ions in aqueous solution. The longer the soaking time of Al powder in water is, the higher the efficiency in removing Cr(VI) is. The effects of Al particle size and dosage, initial Cr(VI) concentration and reaction temperature on Cr(VI) removal were investigated as well. XPS analyses revealed that the decrease in thickness of Al surface passive oxide films and the promotion of surface covered loose Al 2 O 3 phases on hydration of passive oxide films are two main reasons responsible for the rapid removal of Cr(VI) by SM-Al. Meanwhile, SM-Al exhibited an excellent recyclability and the reused SM-Al has a very fast reaction rate relative to as-prepared SM-Al, 80% of Cr(VI) can be removed even it was reused up to five cycles. The present study provides a new route to activate Al in removal of contaminants in aqueous solution. [ABSTRACT FROM AUTHOR]