Surface-adsorbed Molecules Research Articles

Microwave-assisted directional and thermal properties of surface-adsorbed diatomic molecule

Microwave-assisted directional and thermal properties of surface-adsorbed diatomic molecule

Significant Changes in Electrical Resistance of Conductive Porous Silicon Films Produced from Thiol-Modified Silicon Nanoparticle Inks

Materials that reversibly modify their electrical resistance in response to external stimuli have attracted the interest of many researchers due to their potential applications in low-energy consumption memories and memristive devices for constructing electrical neural networks. For example, various chalcogenide glasses, such as Ge2Sb2Te5 [1] and Ag- or In-incorporated Sb2Te [2], can change resistances by 3–6 orders of magnitude, originating from the phase changes between amorphous (high resistance) and crystal (low resistance) states due to rapid and gradual Joule heating. Similar dynamic ranges of resistance changes have been observed in metal-doped glasses [3], such as Ta:Ta2O5, Cu:Ta2O5, Ag:SiO2, Ni:NiO, and nanocomposite Sb-SiO2, using the conductive filament growth/rupture in glasses. Furthermore, devices containing ferroelectric materials, such as Pt/BaTiO3/Nb:SrTiO3 tunnel junctions and Sc-doped AlN/MoS2 ferroelectric field-effect transistors, exhibit similar dynamic ranges by ferroelectric polarization switching.Among these, nanometer-sized Si is a unique material whose resistance can be controlled by near-infrared optical and electrical stimulations [4]. This is the advantage of incorporating resistance change materials into optical communication systems, resulting in the construction of optoelectronic neural networks. However, the following shortcomings of nanometer-sized Si hinder its applications: (1) serious conductivity degradation that proceeds in air and (2) insufficient dynamic ranges of the resistance changes.Recently, we produced sulfur (S)-terminated Si nanoparticles, whose surface is difficult to oxidize even in the air [5]. Because S atoms, which are known to act as donors in Si, are located at the outermost surface of nanoparticles, the electron doping from S atoms can be considerably influenced by the surface-adsorbed molecules. Considering the large surface-to-volume ratio in nanoparticles, the electrical resistances of Si nanoparticle films can potentially be largely changeable through adsorption/desorption of electron-withdrawing molecules, such as O2 and halogens.In this study, we demonstrated that surface S termination considerably reduces resistances in Si nanoparticles, and that S-terminated nanoparticles can reversibly change resistances similar to hitherto reported resistance change materials. Figure 1 shows current–voltage characteristics of the S-terminated Si nanoparticles measured under N2 and O2 atmospheres. As shown in the figure, changing the atmospheric gas significantly altered the current. For example, by changing the atmospheric gas from N2 to O2, the resistance at 2 V changed from 5×106 Ω to greater than 1012 Ω and vice versa. This reversible resistance change is due to O2 adsorption/desorption on the film surface. The electron-withdrawing nature of O2 may induce band bending at the nanoparticle surface as depicted in the figure, and the induced energy barrier may prevent the interparticle transport of electrons, which agrees with the small energy barrier found in our conductive atomic force microscopy measurements. The dynamic range of the resistance change was remarkably comparable to the ranges of the conventional phase change materials, indicating that by terminating the surface with S atoms, Si nanomaterials can be used not only in sensors but also photo-stimulated synaptic devices by controlling the amount of the adsorbed O2, for example, through light irradiation [4].

Solution-Processed TiO2/ZnFe2O4 Heterostructure for Stable Multilevel Memristor with Room-Temperature Reactive Gas Selectivity.

Solution-processed oxide-based heterojunctions that work in diverse directions will be ideal alternatives for cost-effective, stable, and multifunctional devices. Here, we have reported a stable multilevel resistive switching (RS) at the solution-processed TiO2/ZnFe2O4 heterointerface with endurance stability over 104 cycles and retention over 105 s. It can maintain the switching after dripping water onto the device, followed by drying at 100 °C and at an operating temperature of up to 200 °C. As the switching mechanism is governed by filamentary and interface-dominated charge conduction, our device shows additional tunability in the low resistance state (LRS) by changing environmental conditions. The inability to form filaments results in almost negligible switching under a vacuum or inert environment with an LRS loss. Meanwhile, the presence of reducing gas leads to a depletion layer lowering at the TiO2/ZnFe2O4 heterointerface by removing the surface-adsorbed oxygen molecules that help filament conduction through the interface and, hence, a change in LRS. Furthermore, different reaction capacities of different reactive gas environments with the surface-adsorbed oxygen molecule lead to discrete ON-OFF ratios, presenting a pathway to identify several reactive vapors like ammonia, formaldehyde, and acetone at room temperature and presenting a new approach for integrating RS and room temperature gas sensing in the multifunctional device technology.

Theoretical investigation of CO oxidation over polyoxometalate-supported Au cluster catalyst

A polyoxometalate-supported Au cluster catalyst (Au/POM) exhibited high catalytic activity for CO oxidation at room temperature; however, its activity decreased at the reaction temperature above 60 ℃. Density functional theory calculations were performed to elucidate the unique catalytic activities. Our calculations show that the interactions between water molecules accommodated within the defect site of the support and the O2 adsorbed on the Au cluster generate active OOH− species. This OOH− species reacts readily with CO, resulting in high CO oxidation catalytic activity between −40 and 40 degrees Celsius. The activation barrier of CO oxidation over Au/POM in the presence of H2O is much lower than that in the absence of H2O. This is in good agreement with the experimental results, indicating that surface-adsorbed water allows for high CO oxidation catalytic activity around room temperature, whereas the activity decreases at higher temperatures owing to the desorption of surface-adsorbed water molecules.

The role of water in APCI-MS online monitoring of gaseous n-alkanes

In atmospheric pressure chemical ionization mass spectrometry (APCI-MS), [M−3H+H2O]+ ions can deliver analyte-specific signals that enable direct analysis of volatile n-alkane mixtures. The underlying ionization mechanisms have been the subject of open debate, and in particular the role of water is insufficiently clarified to allow for reliable process analytics when the humidity level changes over time. This can be a problem, particularly in online monitoring, where analyte accumulation in the ion source can also occur. Here, we investigated the role of water during APCI-MS of volatile n-alkanes by changing the carrier gas for sample injection from a dry to a wetted state as well as by using 18O-labeled water. This allowed for a distinction between gaseous and surface-adsorbed water molecules. While adsorbed water seems to be responsible for the desired [M−3H+H2O]+ signals through surface reactions with the analyte molecules, gaseous water was found to promote the formation of CnH2n+1O+ of different (and analyte-independent) hydrocarbons, revealing a reaction with hydrocarbon species which accumulated in the ion source during continuous operation. At the same time, gaseous water competed with analyte molecules for ionization and thus suppressed the formation of alkyl (CnH2n+1+) and alkenyl (CnH2n−1+) ions. The results reveal a memory effect due to hydrocarbon adsorption, which may cause severe interpretation difficulties when the ionization chamber undergoes sudden humidity changes. The use of [M−3H+H2O]+ for n-alkane analysis in alkane/water mixtures can be facilitated by constantly maintaining high humidity and hence stabilizing the ionization conditions.Graphical abstract

Water Vapor Condensation in Nanoparticle Films: Physicochemical Analysis and Application to Rapid Vapor Sensing

Nanomaterial-based humidity sensors hold great promise for water vapor detection because of their high sensitivity and fast response/recovery. However, the condensation of water in nanomaterial films remains unclear from a physicochemical perspective. Herein, the condensation of water vapor in silica nanoparticle films was physicochemically analyzed to bridge the abovementioned gap. The morphology of surface-adsorbed water molecules was characterized using infrared absorption spectroscopy and soft X-ray absorption spectroscopy, and the effect of RH on the amount of adsorbed water was observed using a quartz crystal microbalance. The adsorbed water was found to exist in liquid- and ice-like states, which contributed to high and low conductivity, respectively. The large change in film impedance above 80% RH was ascribed to the condensation of water between the nanoparticles. Moreover, RH alteration resulted in a colorimetric change in the film’s interference fringe. The obtained insights were used to construct a portable device with response and recovery times suitable for the real-time monitoring of water vapor. Thus, this study clarifies the structure of water adsorbed on nanomaterial surfaces and, hence, the action mechanism of the corresponding nanoparticle-based sensors, inspiring further research on the application of various nanomaterials to vapor sensing.

New Approaches to Stretched Film Sample Alignment and Data Collection for Vibrational Linear Dichroism.

Rapid measurements of vibrational linear dichroism (VLD) infrared spectra are shown to be possible by using stretched polymer films and an extension of existing instrumentation designed for vibrational circular dichroism spectroscopy. Earlier techniques can be extended using additional inexpensive polymer substrates to record good-quality VLD spectra of a significantly wider range of compounds with comparatively short sample-preparation times. The polymer substrates used, polyethylene and polytetrafluoroethylene, are commonly available and inexpensive, and samples are more easily prepared than that for many earlier stretched-film and crystal studies. Data are presented for neutral hydrophobic organic molecules on hydrophobic films including acridine, anthracene, fluorene, and recently synthesized S-(4-((4-cyanophenyl)ethynyl)phenyl)ethanethioate. We extend the approach to polar or ionic species, including 2,2'-bipyridine, 1,10-phenanthroline, and sodium dodecyl sulfate, by oxidizing polyethylene films to change their wetting properties. The combination of new instrumentation and modified sample preparation methods is useful in basic spectroscopy for untangling and assigning complicated infrared spectra. Nevertheless, it is not a panacea as surface-adsorbed molecules are often not monodispersed, and higher analyte concentrations can lead to aggregation and resonance phenomena that have previously been observed for infrared spectra on surfaces. These effects can be assessed by varying the sample concentration. The focus of this paper is experimental, and detailed analysis of most of the spectra lies outside its scope, including some well-studied compounds such as acridine and anthracene that allow comparisons with earlier research.

Microfluidic delivery of cutting enzymes for fragmentation of surface-adsorbed DNA molecules.

We describe a method for fragmenting, in-situ, surface-adsorbed and immobilized DNAs on polymethylmethacrylate(PMMA)-coated silicon substrates using microfluidic delivery of the cutting enzyme DNase I. Soft lithography is used to produce silicone elastomer (Sylgard 184) gratings which form microfluidic channels for delivery of the enzyme. Bovine serum albumin (BSA) is used to reduce DNase I adsorption to the walls of the microchannels and enable diffusion of the cutting enzyme to a distance of 10mm. Due to the DNAs being immobilized, the fragment order is maintained on the surface. Possible methods of preserving the order for application to sequencing are discussed.

Modeling of intrinsic photon-stimulated desorption yields under readsorption effect

In synchrotron radiation and electron storage rings, photon-stimulated gas desorption is a major contributor to gas load, leading to vacuum degradation and compromising the stability and quality of the beamline. Therefore, it is imperative to investigate the underlying mechanisms of photon-stimulated gas desorption to enhance the reliability of the experiments. In this paper, a theoretical model for analyzing the process of photon-stimulated desorption is presented, and the equations are solved numerically by considering the evacuation, bulk diffusion, thermal outgassing, adsorption, and desorption of surface gas molecules. The modified model can predict the yield of H2 gas desorption induced by photon stimulation when synchrotron radiation is directed vertically onto various sample surfaces, utilizing the coupled multi-physics solution. The calculated results are consistent with the experimental measurements obtained from the Shanghai Synchrotron Radiation Facility. The results show that the photodesorption yield is related to the amount of surface-adsorbed molecules, which explains the observed decrease in the photodesorption yield with increasing accumulated photon dose. Furthermore, the study provides a theoretical approach to predicting the pressure evolution of photon-stimulated desorption.

Distinct Luminescent Thermal Behaviors of Yb3+- and Nd3+-Sensitized Core/Shell Upconversion Nanocrystals

Luminescent materials generally exhibit the thermal quenching due to accelerated nonradiative transitions at elevated temperatures. Recently, the discovery of anomalous thermally induced luminescence enhancement in lanthanide-doped upconversion nanocrystals (UCNCs) has aroused wide attention. The research on this topic not only deepens the understanding on the upconversion luminescence (UCL) mechanism but also promotes frontier applications based on UCNCs. Herein, comparative studies on temperature-dependent UCL properties were performed between Yb3+- and Nd3+-sensitized active-core/active-shell UCNCs. Opposite luminescent thermal behaviors were revealed for these two types of core/shell NCs, and the underlying mechanisms were elucidated with the assistance of temperature-dependent steady/transient spectral analysis under various atmospheres. Yb3+-sensitized active-core/active-shell NCs exhibited an anomalous luminescence enhancement with increasing temperature, which was attributed to the thermally alleviated quenching of surface-adsorbed water molecules. By contrast, Nd3+-sensitized active-core/active-shell NCs showed a normal thermal quenching due to rapidly increased deactivation rates of Nd3+ ions at elevated temperatures, although their UCL intensity was also affected by the quenching effect of surface-adsorbed water molecules. Highly secure anti-counterfeiting patterns were also demonstrated using the nanohybrids of Yb3+- and Nd3+-sensitized core/shell UCNCs as luminescent inks on the basis of their opposite luminescent thermal behaviors. This work provides new insights into luminescent thermal behaviors and energy loss pathways of lanthanide-doped UCNCs.

Toward Imaging Defect-Mediated Energy Transfer between Single Nanocrystal Donors and Single Molecule Acceptors.

Defect-mediated energy transfer is an energy transfer process between midgap electronic states in a semiconductor nanocrystal (NC) and molecular acceptors, such as fluorescent dye molecules. Super-resolution fluorescence microscopy represents an exciting technique for pinpointing the nanoscale positions of lattice defect sites in, for example, a micrometer-sized particle or thin film sample by spatially resolving the location of the acceptor dye molecules with nanometer resolution. Toward this goal, our group performed ensemble-level, time-resolved fluorescence spectroscopy measurements of ZnO NC/Alexafluor 555 (A555) mixtures and calculated that the emissive defect sites are located, on average, 0.5 nm from the NC surface [Nilsson Z. N.; J. Chem. Phys.2021, 154 ( (5), ), 054704]. However, ensemble-level measurements cannot spatially resolve the defect sites on single particles, nor can they distinguish between surface-adsorbed dye molecules that participate in the energy transfer (EnT) process from those that do not. In this work, we compared the photoluminescence intensity trajectories of 789 isolated, single ZnO NC donors to those of 73 non-specifically bound and five specifically bound ZnO NC/A555 pairs, where the donor and acceptor centroid positions were separated by a distance that was smaller than our localization precision (40 nm). We observed minor fluorescence intensity fluctuations in the donor and defect channels instead of clear anticorrelated intensity fluctuations, which could be explained by (1) the presence of multiple emissive defect sites per NC, (2) donor-acceptor separation distances slightly larger than the Förster radius (R 0 = 3.1 nm; defined as the distance at which EnT is 50% efficient), and/or (3) poor dipole-dipole coupling. The single molecule imaging methodology we developed, an alternating ultraviolet-visible excitation sequence combined with multicolor photon detection, successfully distinguishes specifically bound and non-specifically bound NC/dye pairs and can be applied to study a wide range of hybrid NC/dye energy transfer systems.

Pyrochlore cerium stannate (Ce2Sn2O7) for highly sensitive NO2 gas sensing at room temperature

Gas sensing at low temperatures remains a notable challenge at present. Owing to their strong catalytic activity, oxygen defects, and unique size, pyrochlore-based oxides have attracted considerable attention for preparing conductometric gas sensors that are effective at low temperatures. In this study, we prepared a pyrochlore-Ce2Sn2O7 structure using a facile hydrothermal method. The structure, morphology, and surface valance states of the prepared sample were analyzed. Additionally, we investigated the gas-sensing properties, such as the selectivity, response, response and recovery time, repeatability, stability, limit of detection, and influence of relative humidity on the sensing performance for NO2 gas molecules at room temperature (30 ± 2 ℃). The Ce2Sn2O7 exhibited outstanding selectivity for NO2 gas molecules compared with the interfering gas molecules such as N2O, CO, CO2, SO2, NH3,NO and H2S at room temperature (30 ± 2 ℃.). Moreover, the response and recovery time values were 4 s and 52.5 s, respectively, and an outstanding response of 125% was achieved toward 50 ppm NO2 gas molecules. The Ce2Sn2O7 sensor device exhibited excellent repeatability and stability over 90 days. The excellent gas-sensing performance was attributable to the high specific surface area, presence of oxygen vacancies, and surface-adsorbed oxygen molecules.

Near-Infrared Photoluminescence from Ytterbium- and Erbium-Codoped CsPbCl3 Perovskite Quantum Dots with Negative Thermal Quenching.

Near-infrared (NIR) luminescent phosphors hold promise for a wide range of applications, from bioimaging to light-emitting diodes (LEDs), but are typically confined to wavelengths <1300 nm and manifest substantial thermal quenching pervasive in luminescent materials. Here we observed the thermally enhanced NIR luminescence of Er3+ (1540 nm), a 2.5-fold enhancement with increasing temperature from 298 to 356 K, from Yb3+- and Er3+-codoped CsPbCl3 perovskite quantum dots (PQDs) (photoexcited at ∼365 nm). Mechanistic investigations revealed that thermally enhanced phenomena originated from combined effects of thermally stable cascade energy transfer (from a photoexcited exciton to a pair of Yb3+ and then to surrounding Er3+) and minimized quenching of surface-adsorbed water molecules on the 4I13/2 state of Er3+ induced by the temperature increase. Importantly, these PQDs enable producing phosphor-converted LEDs emitting at 1540 nm with inherited thermally enhanced properties, having implications for a wide range of photonic applications.

Development of a sample cell for Radio Frequency µSR studies of metal nanoparticle systems with surface-adsorbed reactants in mesoporous hosts

We have recently begun an investigation of paramagnetic (free-radical) final states formed on metal nanoparticles by muonium (Mu) reactivity with surface-adsorbed molecules. The nanoparticles are incorporated into mesoporous silica, facilitating specific reaction steps in the silica host that involve H-atom transfer reactions important to studies in heterogeneous catalysis. Radio frequency (RF) methods are an essential tool for characterising final state species in these systems, and a non-metallic sample cell is essential for the RF field to penetrate the sample. Unfortunately, several significant problems were encountered during initial experiments using a cell made from PEEK polymer, the most serious being a temporal instability in the signals likely due to reactant molecules adsorbing on the PEEK. This paper discusses the problems encountered using the PEEK cell, and then considers the development of a ceramic cell designed to give better reproducibility in the measurements. The success of this new cell is demonstrated both through off-line tests and by muon measurements, including a series of TF 2G Mu spin precession measurements verifying the temporal stability of the experimental setup. Finally, an RF cavity was fashioned, and RF measurements made for muons stopped in bare silica, with signals from both diamagnetic and paramagnetic muon states clearly seen.

Water is Behind the Electrification of Sand

The results of new experiments indicate that surface-adsorbed water molecules are responsible for contact electrification in granular matter, a finding that challenges established models of this phenomenon.

Defect-Dependent Surface Phase Transformation on 1T-TiS2 Assisted by Water

The phase transformation from the TiS2 to TiS on the surface of bulk 1T-TiS2 crystals is achieved by thermal vacuum annealing. This is demonstrated by a combination of photoemission spectroscopy, electron paramagnetic resonance spectroscopy, and Raman spectroscopy. The chemical interaction between TiS2 and surface-adsorbed H2O molecules is expected to assist this transformation. Especially, the transformation temperature is found to depend on the natural defects present in the TiS2 crystals. Ti interstitial (Tii) and S vacancy (Sv) defects hinder TiS2 to TiS transformation, whereas Ti-OH species facilitate the phase transformation. These results not only provide a valuable insight into the water-assisted phase transformation modulated by defects but also highlight a potential strategy for designing an unusual TiS2-TiS heterostructure through a combination of phase and defect engineering.

Atomically Dispersed Metal–Nitrogen–Carbon Catalysts with d-Orbital Electronic Configuration-Dependent Selectivity for Electrochemical CO2-to-CO Reduction

A variety of atomically dispersed transition-metal-anchored nitrogen-doped carbon (M–N–C) electrocatalysts have shown encouraging electrochemical CO2 reduction reaction (CO2RR) performance, with the underlying fundamentals of central transition-metal atom determined CO2RR activity and selectivity yet remaining unclear. Herein, a universal impregnation-acid leaching method was exploited to synthesize various M–N–C (M: Fe, Co, Ni, and Cu) single-atom catalysts (SACs), which revealed d-orbital electronic configuration-dependent activity and selectivity toward CO2RR for CO production. Notably, Ni–N–C exhibits a very high CO Faradaic efficiency (FE) of 97% at −0.65 V versus RHE and above 90% CO selectivity in the potential range from −0.5 to −0.9 V versus RHE, much superior to other M–N–C (M: Fe, Co, and Cu). With the d-orbital electronic configurations of central metals in M–N–C SACs well elucidated by crystal-field theory, Dewar–Chatt–Duncanson (DCD) and differential charge density analysis reveal that the vacant outermost d-orbital of Ni2+ in a Ni–N–C SAC would benefit the electron transfer from the C atoms in CO2 molecules to the Ni atoms and thus effectively activate the surface-adsorbed CO2 molecules. However, the outermost d-orbital of Fe3+, Co2+, and Cu2+ occupied by unpaired electrons would weaken the electron-transfer process and then impede CO2 activation. In situ spectral investigations demonstrate that the generation of *COOH intermediates is favored over Ni–N–C SAC at relatively low applied potentials, supporting its high CO2-to-CO conversion performance. Gibbs free energy difference analysis in the rate-limiting step in CO2RR and hydrogen evolution reaction (HER) reveals that CO2RR is thermodynamically favored for Ni–N–C SAC, explaining its superior CO2RR performance as compared to other SACs. This work presents a facile and general strategy to effectively modulate the CO2-to-CO selectivity from the perspective of electronic configuration of central metals in M–N–C SACs.

Mass producible, robust SERS substrates based on metal film on nanosphere (MFON) on an adhesive substrate for detection of surface-adsorbed molecules and their evaluation by helium ion microscopy.

We have developed a SERS stamp that can be pressed directly onto a solid surface for characterization of surface-adsorbed target molecules. The stamp was fabricated by transfer of a dense monolayer of SiO2 nanospheres from a glass surface onto a piece of adhesive tape and subsequent evaporation of silver. The performance of the resulting SERS stamps was evaluated by their exposure to methyl mercaptan vapor, and immersion in rhodamine 6G and ferbam solutions. It was found that beside the nanosphere diameter and metal deposition thickness, the extent of burial of the nanospheres into the adhesive tape, dictated by the pressure during the nanosphere transfer process, had a significant effect. We carried out FDTD calculations of the near field. Models are based on morphological information obtained from helium ion microscopy, which can provide high-resolution images of poor electrical conductors such as our SERS stamp. While one of our main eventual goals is detection of pesticides on agricultural produce, we have begun to take a careful step by testing our SERS stamp on better characterized surfaces such as a porous gel surface, having been immersed in fungicides such as ferbam. We also present our preliminary results with ferbam on oranges. It is expected that our well-characterized SERS stamp will play a role in shedding light on the poorly studied transfer process of target molecules onto a SERS surface as well as serving as a new SERS platform.

Understanding Oligonucleotide Hybridization and the Role of Anchoring on the Single-Walled Carbon Nanotube Corona Phase for Viral Sensing Applications

Semiconducting single-walled carbon nanotubes (SWCNTs) with tailored corona phases (CPs), or surface-adsorbed molecules, have emerged as a promising interface for sensing applications. The adsorption of an analyte can be specifically transduced as a modulation of their band-gap near-infrared (nIR) photoluminescence (PL). One such CP ideal for this purpose is single-stranded DNA (ssDNA), where subsequent sequence-dependent hybridization can result in PL emission wavelength shifts. Due to ssDNA adsorption to the SWCNT surface, the resultant noncanonical hybridization and its effect on SWCNT photophysical properties are not well understood. In this work, we study 20- and 21-mer DNA and RNA hybridization on the complementary ssDNA-SWCNT CP in the context of nucleic acid sensing for SARS-CoV-2 sequences as model analytes. We found that the van’t Hoff transition enthalpy of hybridization on SWCNT CP was −11.9 kJ mol–1, much lower than that of hybridization in solution (−707 kJ mol–1). We used SWCNT solvatochromism to calculate the solvent-exposed surface area to indicate successful hybridization. We found that having a 30-mer anchor region in addition to the complementary region significantly improved PL response sensitivity and selectivity, with a (GT)15 anchor preferred for RNA targets. Coincubation of ssDNA-SWCNTs with an analyte at 37 °C resulted in faster hybridization kinetics without sacrificing specificity. Other methods aimed to improve CP rearrangement kinetics such as bath sonication and surfactant additions were ineffective. We also determined that the target sequence choice is important as secondary structure formation in the target is negatively correlated with hybridization. Best-performing CPs showed detection limits of 11 and 13 nM for DNA and RNA targets, respectively. Finally, we simulated sensing conditions using the saliva environment, showing sensor compatibility in biofluids. In total, this work elucidates key design features and processing to enable sequence-specific hybridization on ssDNA-SWCNT CPs.

Integrated Adsorption-Photocatalytic Decontamination of Oxytetracycline from Wastewater Using S-Doped TiO2/WS2/Calcium Alginate Beads

Integrated wastewater treatment processes are needed due to the inefficient removal of emerging pharmaceuticals by single methods. Herein, an adsorbent-photocatalyst integrated material was fabricated by coupling calcium alginate with sulfur-doped TiO2/tungsten disulfide (S-TiO2/WS2/alginate beads) for the removal of oxytetracycline (OTC) from aqueous solution by an integrated adsorption-photocatalysis process. The semiconductor S-TiO2/WS2 hybrid photocatalyst was synthesized with a hydrothermal method, while the integrated adsorbent-photocatalyst S-TiO2/WS2/alginate beads were synthesized by blending S-TiO2/WS2 with sodium alginate using calcium chloride as a precipitating agent. The physicochemical characteristics of S-TiO2/WS2/alginate beads were analyzed using X-ray diffraction , scanning electron microscopy, elemental mapping, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. The integrated adsorption-photocatalysis process showed enhanced removal from 92.5 to 72%, with a rise in the OTC concentration from 10 to 75 mg/L respectively. The results demonstrated that the adsorption of OTC onto S-TiO2/WS2/alginate beads followed the Elovich kinetic model and Redlich–Peterson isotherm models. The formations of H-bonds, cation bridge bonding, and n-π electron donor-acceptor forces were involved in the adsorption of OCT onto S-TiO2/WS2/alginate beads. In the integrated adsorption-photocatalysis, surface-adsorbed OTC molecules were readily decomposed by the photogenerated active radical species (h⁺, O2•−, and HO•). The persulfate addition to the OTC solution further increased the photocatalysis efficacy due to the formation of additional oxidizing species (SO4•⁻, SO4⁻). Moreover, S-TiO2/WS2/alginate beads showed favorable efficiency and sustainability in OTC removal, approaching 78.6% after five cycles. This integrated adsorption-photocatalysis process offered significant insight into improving efficiency and reusability in water treatment.