Combined Chemical Activation and Fenton Degradation to Convert Waste Polyethylene into High-Value Fine Chemicals.

Plastic waste is a valuable organic resource. However, proper technologies to recover usable materials from plastic are still very rare. Although the conversion/cracking/degradation of certain plastics into chemicals has drawn much attention, effective and selective cracking of the major waste plastic polyethylene is extremely difficult, with degradation of C-C/C-H bonds identified as the bottleneck. Pyrolysis, for example, is a nonselective degradation method used to crack plastics, but it requires a very high energy input. To solve the current plastic pollution crisis, more effective technologies are needed for converting plastic waste into useful substances that can be fed into the energy cycle or used to produce fine chemicals for industry. In this study, we demonstrate a new and effective chemical approach by using the Fenton reaction to convert polyethylene plastic waste into carboxylic acids under ambient conditions. Understanding the fundamentals of this new chemical process provides a possible protocol to solve global plastic-waste problems.

Synthesis of a New Bimetallic Re(I)-NCS-Pt(II) Complex as Chemodosimetric Ensemble for the Selective Detection of Mercapto-Containing Pesticides.

Detection of mercapto-containing pesticides plays a crucial role in food and water safety. A new Re(I)-NCS-Pt(II) complex, [Re(4,4'-di-tert-butyl-2,2'-bipyridine)(CO)3(NCS)]-[Pt(DMSO)(Cl)2] (1), was synthesized and characterized. The synthetic procedure, characterization results, and photophysical data for 1 are reported in this paper. Solvated complex 1 demonstrated luminescent chemodosimetric selectivity for phorate, demeton, and aldicarb (three common mercapto-containing pesticides) with method detection limits (MDLs) of 1.00, 2.87, and 2.08 ppm, respectively. The binding constants (log K) of 1 toward them were in the 3.24-3.44 range. The analyte selectivity of the complex was found to be dependent on the bridging linkage (C≡N and N═C═S) between the Re(I) and Pt(II) centers. The solid-supported dosimetric device 1 was fabricated by blending complex 1 with Al2O3 and poly(vinyl chloride) (PVC) powder. The MDLs of the device toward the mercapto-containing pesticides were 0.48-0.60 ppm. The device was applicable to pesticides in real water bodies such as taps, rivers, lakes, and underground water bodies with excellent recoveries and relative standard deviations of 76.2-108.0% and 2.9-6.7%, respectively. Its spectrofluorimetric changes could be analyzed by naked eye within 20 min with a linear luminometric response toward increases in the phorate concentration (0-8.0 ppm) with R = 0.999.

The solvent effect and identification of a weakly emissive state in nonradiative dynamics of guanine nucleosides and nucleotides--a combined femtosecond broadband time-resolved fluorescence and transient absorption study.

A combined method of femtosecond broadband time-resolved fluorescence (fs-TRF) and transient absorption (fs-TA) was employed to investigate the excited state dynamics of 2'-deoxyguanosine (dG) and 2'-deoxyguanosine 5'-monophosphate (dGMP). Comparative fs-TRF and fs-TA measurements were conducted on dG and dGMP in neutral water, deuterated water, and methanol with excitation wavelengths of 245, 267 and 285 nm. Very similar results were observed with dG and dGMP. The data provide compelling evidence for the co-existence of two nonradiative pathways. One is the generally recognized Laππ* mediated channel, the other involves an unprecedented weakly emissive state which plays a significant role in the overall deactivation processes. The Laππ* channel features biphasic dynamics with time constants (τ1/τ2) of ~0.2/0.8 ps in water and ~0.25/1.0 ps in methanol. The biphasic decay arises due to a partial transfer with τ1 of the Laππ* population to the newly identified state followed by conversion in τ2 of the remaining Laππ* molecules into the electronic ground state. The channel mediated by the weakly emissive species shows solvent-dependent dynamics with time constants (τ3) of ~2.0 ps in water, ~2.3 ps in deuterated water, and ~4.1 ps in methanol. The species features absorption at UV wavelengths (~300-400 nm) and exhibits deeply red-shifted fluorescence (λmax ~ 520 nm) with polarization direction varied markedly from that of the Laππ* but close to the Lbππ*. This species acts as an effective quenching state to the radiative decay of the brightly emissive Laππ* and Lbππ*. It sets in promptly (<~50 fs) after the photoexcitation and is further populated through nonadiabatic coupling with the Laππ*. The overall involvement of this state is facilitated with excitation at high energy and is favoured in methanol over water. According to the spectral character and the solvent effect in particular the kinetic isotope effect, the species is tentatively associated to the πσ* state with charge transfer (CT) character which is considered to be preferentially stabilized by hydrogen-bonding between the guanine amino and surrounding solvent molecules. The result of this study leads to a dramatically different picture of guanine deactivation. It demonstrates a crucial role of the solvent in shaping the nonradiative dynamics of guanine nucleosides and nucleotides. The data presented are important for understanding the detailed photophysics of not only the monomeric guanine but also DNA assemblies that contain guanine in base pairs or have a guanine tetrad as the structural motif.

Femtosecond broadband time-resolved fluorescence and transient absorption study of the intramolecular charge transfer state of methyl 4-dimethylaminobenzoate.

A combined application of femtosecond broadband time-resolved fluorescence (fs-TRF), fluorescence anisotropy (fs-TRFA) and fs to microsecond (µs) transient absorption (TA) have been used to probe directly the dynamics, nature, formation and decay paths of the singlet intramolecular charge transfer ((1)ICT) state of methyl 4-dimethylaminobenzoate (1a) in acetonitrile. The result reveals explicit evidence for a common electronic origin (the L(a) nature) of the (1)ICT state and its precursor the locally excited ((1)LE) state to account jointly for the dual florescence known to this system. It also shows that the ICT reaction from the (1)LE to (1)ICT state occurs with time constant of ~0.8 ps and the (1)ICT state formed decays with a ~1.9 ns time constant leading mainly to a ππ* natured triplet state ((3)T(1)). The (3)T(1) then relaxes with a ~4 µs lifetime under deoxygenated condition resulting in full recovery of the ground state (S(0)). As a case study, this work contributes novel experimental data for improved understanding of the mechanism of ICT reaction; it also reveals a distinct deactivation pattern for this prototype para-amino substituted aromatic carbonyl compound in acetonitrile.

A highly sensitive ultraviolet sensor based on a facile in situ solution-grown ZnO nanorod/graphene heterostructure.

The weak photon absorption and fast carrier kinetics of graphene limit its application in photodetection. This limitation can be overcome by introducing photosensitive nanostructures to graphene. Herein we report the synthesis of a ZnO nanorod/graphene heterostructure by a facile in situ solution growth method. By combining the attributes of photosensitive ZnO nanorods and highly conductive graphene, we for the first time demonstrate a highly sensitive visible-blind ultraviolet (UV) sensor based on graphene related heterostructure. The photoresponsibility of the UV sensor can reach 22.7 A W(-1), which is over 45,000 fold higher than that of single graphene sheet based photodetectors.