In the present study,
alkaline earth metal scheelite-type ABO4 compounds (A =
Ca, Sr, and Ba; B = Mo and W) synthesized
by a hydrothermal method were systematically studied. The as-obtained
photocatalysts were characterized by X-ray diffraction (XRD), scanning
electron microscopy (SEM), Brunauer–Emmett–Teller (BET)
surface area analysis, UV–vis diffuse reflectance (DR/UV–vis)
spectroscopy, photoluminescence, and thermoluminescence (TL) spectroscopy
together with charge carrier lifetime measurements, electron paramagnetic
resonance (EPR) spectroscopy, and electrochemical impedance spectroscopy
(EIS). The photocatalytic activity was studied in the reaction of
phenol degradation under simulated solar light. The obtained tungstates
and molybdates revealed excellent photocatalytic activity despite
the low surface area and wide bandgap typical for insulators. The
mechanism of phenol degradation proceeded through hydroquinone and
catechol formation in the presence of hydroxyl and superoxide radicals.
The presence of electron traps allowed absorption of light with lower
energy than resulting from the absorption edge. BaWO4 and
SrWO4, with the most extended average carrier lifetime,
were the most efficient photocatalysts from the obtained series. In
general, molybdates exhibited lower photocatalytic activity toward
phenol degradation due to deeper trap states and lower average charge
carrier lifetimes than tungstates. Additionally, electrochemical studies
demonstrated that molybdates exhibit more insulating behavior than
tungstates. The overall results showed that wide-bandgap semiconductors,
mainly tungstates, can be applied as earth-abundant photocatalytic
materials for the degradation of persistent organic pollutants.
Reaching
the corneal endothelium through the topical administration
of therapeutic drugs remains a challenge in ophthalmology. Besides,
endothelial cells are not able to regenerate, and diseases at this
site can lead to corneal blindness. Targeting the corneal endothelium
implies efficient penetration through the three corneal layers, which
still remains difficult for small molecules. Carbon quantum dots (CQDs)
have demonstrated great potential for ocular nanomedicine. This study
focuses on the corneal penetration abilities of differently charged
CQDs and their use as permeation enhancers for drugs. Excised whole
bovine eyes were used as an ex vivo model to investigate
corneal penetration of CQDs derived from glucosamine using β-alanine,
ethylenediamine, or spermidine as a passivation agent. It was found
that negatively charged CQDs have limited corneal penetration ability,
while positively charged CQDs derived from glucosamine hydrochloride
and spermidine (CQD-S) penetrate the entire corneal epithelium all
the way down to the endothelium. CQD-S were shown to enhance the penetration
of FITC-dextran 150 kDa, suggesting that they could be used as efficient
penetration enhancers for therapeutic delivery to the corneal endothelium.
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