The Brønsted/Lewis acid synergy in dealuminated HY zeolite has been studied using solid-state NMR and density function theory (DFT) calculation. The 1H double quantum magic-angle spinning (DQ-MAS) NMR results have revealed, for the first time, the detailed spatial proximities of Lewis and Brønsted acid sites. The results from 13C NMR of adsorbed acetone as well as DFT calculation demonstrated that the Brønsted/Lewis acid synergy considerably enhanced the Brønsted acid strength of dealuminated HY zeolite. Two types of Brønsted acid sites (with enhanced acidity) in close proximity to extra-framework aluminum (EFAL) species were identified in the dealuminated HY zeolite. The NMR and DFT calculation results further revealed the detailed structures of EFAL species and the mechanism of Brønsted/Lewis acid synergy. Extra-framework Al(OH)3 and Al(OH)2+ species in the supercage cage and Al(OH)2+ species in the sodalite cage are the preferred Lewis acid sites. Moreover, it is the coordination of the EFAL species to the oxygen atom nearest the framework aluminum that leads to the enhanced acidity of dealuminated HY zeolite though there is no direct interaction (such as the hydrogen-bonding) between the EFAL species and the Brønsted acid sites. All these findings are expected to be important in understanding the roles of Lewis acid and its synergy with the Brønsted acid in numerous zeolite-mediated hydrocarbon reactions.

Zeolites are widely used in various acid-catalyzed reactions (e.g., cracking, disproportionation, isomerization, and alkylation) in the chemical and petrochemical industry due to their peculiar pore structure, strong acidity, and high selectivity. [1][2][3][4] Since the catalytic activity and selectivity of dealuminated zeolites are much higher than those of their respective parents, zeolite modification by dealumination has received considerable attention. [5][6][7] In zeolites, fourcoordinate framework aluminum (FAL) is associated with a Brønsted acid site (SiOHAl), while extra-framework aluminum (EFAL) species generated during the dealumination process acts as a Lewis acid site. The existence of EFAL species is crucial for a favorable influence on the catalytic properties of zeolites.[8] Although enormous progress has been made in the studies of the nature of both FAL and EFAL by various methods, including solid-state NMR spectroscopy, [9] X-ray standing waves, [10] X-ray absorption near edge structure, [11] and theoretical calculations, [12] the detailed structure of EFAL species and the spatial proximities (or interactions) of various Al species in dealuminated zeolites are poorly understood. This strongly hampers the understanding of structure-activity relationship in numerous zeolites.One-dimensional single-pulse 27 Al MAS NMR and twodimensional multiple-quantum magic angle spinning (MQ-MAS) NMR have been used extensively to study the local symmetry and coordination state of aluminum species in zeolites. [13][14][15] However, both are unable to obtain information on the spatial correlation of different aluminum species. Twodimensional 27 Al double-quantum MAS NMR (DQ-MAS NMR) is a powerful technique for probing aluminumaluminum proximities in solid materials. However, the 27 Al DQ-MAS NMR technique still remains a great challenge because of the quadrupolar nature of the aluminum nucleus (I = 5/2), which leads to low efficiency of DQ excitation (< 5 %). So far, the 27 Al DQ-MAS NMR technique has been successfully applied to systems with high Al content, such as aluminophosphate molecular sieves, [16][17][18] glasses, [19] and minerals, [20] but for aluminosilicate zeolites with low Al content, the technique was less successful due to its extremely low sensitivity. [21] Homonuclear dipolar recoupling of quadrupolar nuclei under MAS is difficult because of the intricate nuclear spin dynamics of the quadrupolar nuclei in the presence of an rf field and sample rotation. Mali et al. first demonstrated that the rotary resonance recoupling (R 3 ) technique with HORROR condition [22] can be used for DQ recoupling of half-integer quadrupolar nuclei. [16,23] As an improvement, EdØn et al. then showed that symmetry-based pulse sequences display superior rf error tolerance than HORROR recoupling, and these sequences were incorporated into DQ-MAS experiments. [17,20] Recently, we developed a new homonuclear 27 Al DQ-MAS NMR correlation method based on the rotor-synchronized and symmetry-based BR2

The spatial proximities of acid sites in dealuminated H–MOR and H–ZSM-5 zeolites have been comprehensively studied by two-dimensional 1H and 27Al double-quantum magic-angle spinning (DQ-MAS) NMR spectroscopy. 1H DQ-MAS NMR revealed the detailed spatial proximities among Brønsted and Lewis acid sites, while 27Al DQ-MAS NMR probed the detailed spatial proximities among various aluminum species in the dealuminated zeolites. It was found that all of the extra-framework aluminum species (EFAL, Lewis acid sites) are always in close proximity to the framework aluminum (Brønsted acid sites) in both H–MOR and H–ZSM-5 zeolites. The result from 13C CP/MAS NMR of adsorbed acetone demonstrated that the spatial proximities between Brønsted and Lewis acid sites lead to a synergy effect that can remarkably enhance the Brønsted acid strength of the dealuminated zeolites. On the basis of these experimental results, we proposed a model to describe the Brønsted/Lewis acid synergy in the dealuminated zeolites.

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Lignin-based graphene quantum dots are fabricated by a two-step bottom up method and their fluorescence mechanism is elaborated by DFT calculations.

Nanoparticles are being increasingly recognized for their potential utility in biological applications including nanomedicine. The aim of this study is to investigate a new strategy to combine the ZnO nanoparticles with graphene for targeting photodynamic therapy (PDT) under visible light irradiation. Folic acid (FA), a targeting agent toward tumor cells, was conjugated onto graphene oxide (GO) via imide linkage. Using a simple and effective chemical precipitation method, a GO-FA-ZnO nanohybrid was then prepared. The combination of ZnO with GO-FA induced a remarkable improvement in tumor targeting, which has been demonstrated by the cellular uptake assay. Due to the high electrical conductivity of graphene, the interaction between graphene and ZnO, and the inhibition of aggregation, the hybrid of GO-FA and ZnO significantly enhances the photodynamic activity. It was noted that the photodynamic activity of the non-cytotoxic GO-FA-ZnO is mediated by reactive oxygen species (ROS) generation under visible light irradiation. Following the ROS generation, GO-FA-ZnO caused a significant decrease in cell viability, mitochondrial membrane potential, superoxide dismutase activity, catalase and glutathione peroxidase, as well as an increase in malonodialdehyde production.Moreover, GO-FA-ZnO induced apoptotic death by elevating the caspase-3 activity. The study presents a novel tumor targeting photosensitizer and a promising strategy in PDT for cancer treatment.

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Bright long-wavelength-excitable semiconducting polymer dots (LWE-Pdots) are highly desirable for in vivo imaging and multiplexed in vitro bioassays.L WE-Pdots have been obtained by incorporating an ear-infrared (NIR) emitter into the backbone of ap olymer host to develop ab inary donor-acceptor (D-A) system. However,t hey usually suffer from severe concentration quenching and at rade-off between fluorescence quantum yield (F f )a nd absorption cross-section (s). Herein, we describe at ernary component (D 1 /D 2 -A) strategy to achieve ultrabright, green laser-excitable Pdots with narrow-band NIR emission by introducing aB ODIPY-based assistant polymer donor as D 1 .T he D 1 /D 2 -A Pdots possess improved F f and s compared to corresponding binary D 2 -A Pdots.T heir F f is as high as 40.2 %, one of the most efficient NIR Pdots reported. The D 1 /D 2 -A Pdots show ultrahigh single-particle brightness,83-fold brighter than Qdot 705 when excited by a5 32 nm laser.W hen injected into mice,h igher contrast in vivo tumor imaging was achieved using the ternary Pdots versus the binary D-A Pdots.