Hydroxyapatite-Coated Screws Versus Titanium Triangular Dowels for Sacroiliac Joint Fusion: Results From a Nonrandomized Prospective Outcome Study.

OBJECTIVE: This is a single-surgeon series that prospectively evaluates the results of sacroiliac joint (SIJ) fusion for patients with SIJ dysfunction using hydroxyapatite-coated screws (HACSs) compared with titanium triangular dowels (TTDs). METHODS: A total of 113 patients underwent SIJ fusion surgery between 2013 and 2018 at the University Hospital Llandough to treat symptomatic SIJ dysfunction not responding to nonoperative measures. Of the 113 patients, 40 were treated with HACSs and 73 with TTDs. Patient-reported outcomes measures (PROMs) were collected preoperatively and at 12 months postoperatively, including the 36-item short-form health survey, Oswestry disability index, EuroQol-5D-5L, and Majeed pelvic score. Patients with ongoing symptoms were followed up beyond the study period. RESULTS: Of the 113 patients, 33 completed follow-up in the HACS group compared with 61 in the TTD group. Both groups had comparable preoperative PROMs; however, the postoperative PROMs were significantly better in the TTD group. Additionally, 21 patients (63%) in the HACS group had radiological evidence of screw lysis compared with 5 patients (9%) in the TTD group. A subgroup analysis revealed less significant improvement in PROMs for patients with screw lysis compared with those without. Four patients were offered further revision surgery. CONCLUSIONS: Minimally invasive SIJ fusion has been shown to have good clinical outcomes for select patients. However, our experience shows that HACSs are associated with a high rate of screw lysis and poorer patient outcomes compared with TTDs. Therefore, we recommend the use of TTDs instead of HACSs for SIJ fusion surgery.

Unusual Mechanism of Injury during a Wedding Tradition Leading to a Metacarpal Shaft Fracture - A Case Report.

Introduction: "Joota Chori" is a traditional Indian wedding ritual which involves playful competition between the bride's and the groom's friends, with the aim of hiding and retrieving the groom's shoes. Case Report: We describe a rare case scenario wherein an orthopedic surgeon sustained a metacarpal shaft fracture while gripping the shoe and engaging in a tussle with the groom's friends. Despite feeling a sudden snap and experiencing pain, the surgeon held onto the shoe. The subsequent diagnosis revealed a 4th metacarpal long oblique shaft fracture. Conclusion: This case highlights the uncommon mechanism of injury involving forceful hyperextension of the MCP joint and the potential risks associated with physically intense wedding rituals. It also emphasizes the importance of adequate first aid resources and medical attention at wedding venues to promptly address musculoskeletal injuries.

Intraprosthetic Dislocation of Dual Mobility Total Hip Arthroplasty: A Case Report and Review of Literature.

Introduction: First introduced in Europe in the 1970s, dual mobility total hip arthroplasty (DM-THA) has gained popularity over years due to the reduced dislocation rates compared to standard THA. However, intraprosthetic dislocation (IPD), a rare complication where the femoral head separates from the polyethylene (PE) liner, remains a potential complication. Case Report: A 67-year-old female presented with a transcervical neck of femur fracture. She was managed with a DM-THA. She dislocated her THA on post-operative day 18. Closed reduction was performed for the same under general anesthesia. However, she again dislocated her hip 2 days later. CT scan was done and an IPD was diagnosed. The PE liner was revised and the patient had a good outcome at 1 year follow-up. Conclusion: When a DM-THA dislocates, it is important to consider the possibility of IPD which is a rare but unique complication associated with these systems. The recommended treatment for IPD is open reduction and replacement of the PE liner.

Inverse kinetic isotope effects in the oxygen reduction reaction at platinum single crystals.

Although the oxygen reduction reaction (ORR) involves multiple proton-coupled electron transfer processes, early studies reported the absence of kinetic isotope effects (KIEs) on polycrystalline platinum, probably due to the use of unpurified D2O. Here we developed a methodology to prepare ultra-pure D2O, which is indispensable for reliably investigating extremely surface-sensitive platinum single crystals. We find that Pt(111) exhibits much higher ORR activity in D2O than in H2O, with potential-dependent inverse KIEs of ~0.5, whereas Pt(100) and Pt(110) exhibit potential-independent inverse KIEs of ~0.8. Such inverse KIEs are closely correlated to the lower *OD coverage and weakened *OD binding strength relative to *OH, which, based on theoretical calculations, are attributed to the differences in their zero-point energies. This study suggests that the competing adsorption between *OH/*OD and *O2 probably plays an important role in the ORR rate-determining steps that involve a chemical step preceding an electrochemical step (CE mechanism).

Coverage-Dependent Rate-Driving Force Relationships: Hydrogen Transfer from Cerium Oxide Nanoparticle Colloids.

Rate-driving force relationships, known as Brønsted-Evans-Polanyi (BEP) relations, are central to many methods for predicting the performance of heterogeneous catalysts and electrocatalysts. Methods such as Tafel plots and "volcano" analyses often assume that the effect of adsorbate coverage on reaction rates across different materials is constant and known. Here, we use UV-visible spectroscopy to test these assumptions by measuring rates of net hydrogen atom transfer from colloidal cerium oxide nanoparticles (nanoceria) to organic reagents at varying surface CeO-H bond strengths and surface coverages. The resulting rate constants follow a linear BEP relationship, Δlog(k) = αΔlog(Keq), across two sizes of nanoceria, two organic reagents, and a ∼10 kcal mol-1 range of CeO-H bond strengths. Interestingly, the Brønsted slope is only 0.2, demonstrating that the rate constants are far less sensitive to CeO-H bond strength than would commonly be assumed for a heterogeneous nanomaterial. Furthermore, we observe a Brønsted slope >1 when altering the reaction driving force via the organic reagent bond strength instead of that of CeO-H. The implications of these Brønsted slopes for either concerted or stepwise mechanisms are discussed. To our knowledge, these are the first solution-phase measurements of BEP relationships for hydrogen coverage on a (nano)material.

Referrals from community optometrists in England and their replies: A mixed methods study.

PURPOSE: Community optometrists, through routine eye examinations, identify patients with disease or ocular abnormalities requiring referral to the Hospital Eye Service. In many cases no reply to the referral letter is received, resulting in some patients being re-referred unnecessarily, potentially increasing the number of other patients who lose sight whilst on hospital waiting lists. This study investigated, qualitatively and quantitatively, factors influencing optometric referrals and replies. METHODS: The three-phase, sequential mixed methods study started with a literature review and qualitative phase, interviewing stakeholders to identify issues for exploration in subsequent phases. The second, quantitative phase, undertook documentary analysis of 349 patient referral records from three optometric practice modalities (domiciliary, independently owned, and corporate chain) in England. A final qualitative phase obtained views from stakeholders to explore unexplained findings from the first two phases. RESULTS: Phase 1 identified communication, financial, professional and technological issues for further exploration. In Phase 2, the referral rate was 22.2% for domiciliary provider, 2.1% for independent practice and 2.5% for the corporate chain, with the variation most likely explained by patient age and associated ophthalmic disease, illness and disability. The referral reply rate was 5.7% for domiciliary provider, 25.0% for independent practice and 4.9% for the corporate chain. The community optometrist remained unaware of the outcome of their referral in 72.8% of cases. Qualitative analyses indicate the main factors influencing referral reply rates are technology, the General Medical Practitioner, community optometrists' utility to and utility of the National Health Service and patient mobilisation. CONCLUSIONS: The low referral reply rate creates a break in the feedback loop required to raise the standard of referrals and avoid unnecessary re-referral. Of the factors identified that influence referral reply rates, technology is key in view of the increasing use of online referral platforms. Feedback to the referring optometrist should be embedded in such systems.

Free Energies of Proton-Coupled Electron Transfer Reagents and Their Applications.

We present an update and revision to our 2010 review on the topic of proton-coupled electron transfer (PCET) reagent thermochemistry. Over the past decade, the data and thermochemical formalisms presented in that review have been of value to multiple fields. Concurrently, there have been advances in the thermochemical cycles and experimental methods used to measure these values. This Review (i) summarizes those advancements, (ii) corrects systematic errors in our prior review that shifted many of the absolute values in the tabulated data, (iii) provides updated tables of thermochemical values, and (iv) discusses new conclusions and opportunities from the assembled data and associated techniques. We advocate for updated thermochemical cycles that provide greater clarity and reduce experimental barriers to the calculation and measurement of Gibbs free energies for the conversion of X to XHn in PCET reactions. In particular, we demonstrate the utility and generality of reporting potentials of hydrogenation, E°(V vs H2), in almost any solvent and how these values are connected to more widely reported bond dissociation free energies (BDFEs). The tabulated data demonstrate that E°(V vs H2) and BDFEs are generally insensitive to the nature of the solvent and, in some cases, even to the phase (gas versus solution). This Review also presents introductions to several emerging fields in PCET thermochemistry to give readers windows into the diversity of research being performed. Some of the next frontiers in this rapidly growing field are coordination-induced bond weakening, PCET in novel solvent environments, and reactions at material interfaces.

Results From an All Wales Trainee Led Collaborative Prospective Audit on Management of Ankle Fractures.

Aim The purpose of this all Wales national audit was to compare compliance against British Orthopedic Association Standards for Trauma (BOAST) guidelines on the management of ankle fractures. Methods A multi-center prospective audit of the management of adult ankle fractures was conducted between February 2, 2020, and February 17, 2020, via the Welsh Orthopedic Research Collaborative (WORC). Regional leads were recruited in nine NHS hospitals across six university health boards, and recruited collaborators in their respective hospitals. Questionnaires for the data collection on both surgical and conservative management were made available via a password-protected website (walesortho.co.uk). We defined early weight-bearing (EWB) as unrestricted weight-bearing on the affected leg within three weeks of injury or surgery and delayed weight-bearing (DWB) as unrestricted weight-bearing after three weeks of injury or surgery. Results A total of 28 collaborators contributed data for 238 ankle fractures. Poor documentation at the time of injury was noted. Less than 50% of patients with posterior malleolus fracture had a CT scan for further evaluation. Eighty-four percent of the non-operatively treated patients did not have a weight-bearing X-ray (WBXR). Patients who had a WBXR were more likely to be allowed EWB but this was not statistically significant. EWB was allowed in 59.43% and 10% of the non-operatively and operatively treated patients, respectively. DWB was higher in patients who had fixation of the posterior malleolus or syndesmosis. Conclusion There is poor compliance with BOAST guidelines on the management of ankle fractures across Wales. We need to improve documentation and also consider performing a CT scan when the posterior malleolus is fractured. A weight-bearing X-ray should be performed more often to ascertain the stability of an ankle fracture, and those that are deemed stable should be treated with early weight-bearing. The guidelines need to be clearer regarding weight-bearing after fixation especially when posterior malleolus and/or syndesmosis are fixed.

A Compressed Sensing Approach to Pooled RT-PCR Testing for COVID-19 Detection.

We propose 'Tapestry', a single-round pooled testing method with application to COVID-19 testing using quantitative Reverse Transcription Polymerase Chain Reaction (RT-PCR) that can result in shorter testing time and conservation of reagents and testing kits, at clinically acceptable false positive or false negative rates. Tapestry combines ideas from compressed sensing and combinatorial group testing to create a new kind of algorithm that is very effective in deconvoluting pooled tests. Unlike Boolean group testing algorithms, the input is a quantitative readout from each test and the output is a list of viral loads for each sample relative to the pool with the highest viral load. For guaranteed recovery of [Formula: see text] infected samples out of [Formula: see text] being tested, Tapestry needs only [Formula: see text] tests with high probability, using random binary pooling matrices. However, we propose deterministic binary pooling matrices based on combinatorial design ideas of Kirkman Triple Systems, which balance between good reconstruction properties and matrix sparsity for ease of pooling while requiring fewer tests in practice. This enables large savings using Tapestry at low prevalence rates while maintaining viability at prevalence rates as high as 9.5%. Empirically we find that single-round Tapestry pooling improves over two-round Dorfman pooling by almost a factor of 2 in the number of tests required. We evaluate Tapestry in simulations with synthetic data obtained using a novel noise model for RT-PCR, and validate it in wet lab experiments with oligomers in quantitative RT-PCR assays. Lastly, we describe use-case scenarios for deployment.

Timing of Intubation in Coronavirus Disease 2019: A Study of Ventilator Mechanics, Imaging, Findings, and Outcomes.

OBJECTIVES: Determine the variation in outcomes and respiratory mechanics between the subjects who are intubated earlier versus later in their coronavirus disease 2019 course. DESIGN: Retrospective cohort study. SETTING: Northwestern Memorial Hospital ICUs. PATIENTS: All patients intubated for coronavirus disease 2019 between March 2020 and June 2020. INTERVENTIONS: Patients were stratified by time to intubation: 30 subjects were intubated 4-24 hours after presentation and 24 subjects were intubated 5-10 days after presentation. Baseline characteristics, hospitalization, ventilator mechanics, and outcomes were extracted and analyzed. Ten clinically available CT scans were manually reviewed to identify evidence of pulmonary vascular thrombosis and intussusceptive angiogenesis. MEASUREMENTS AND MAIN RESULTS: Median time from symptom onset to intubation was significantly different between the early and late intubation cohorts, with the latter being intubated later in the course of their illness (7.9 vs 11.8 d; p = 0.04). The early intubation cohort had a lower mortality rate than the late intubation cohort (6% vs 30%, p < 0.001) without significantly different respiratory mechanics at the time of intubation. The late intubation cohort was noted to have higher dead space ratio (0.40 vs 0.52; p = 0.03). On review of CT scans, the late intubation cohort also had more dilated peripheral segments on imaging (two segments vs five segments). CONCLUSIONS: The question as to whether delaying intubation is beneficial or harmful for patients with coronavirus disease 2019-induced hypoxemic respiratory failure has yet to be answered. As our approaches to coronavirus disease 2019 continue to evolve, the decision of timing of intubation remains paramount. Although noninvasive ventilation may allow for delaying intubation, it is possible that there are downstream effects of delayed intubation that should be considered, including the potential for pulmonary vascular thrombosis and intussusceptive angiogenesis with delayed intubation.

Outcome Analysis of Subaxial Cervical Spine Tuberculosis Operated by the Anterior Approach: A Single-Center Experience.

BACKGROUND: Though spinal tuberculosis has a predilection for the dorsal and lumbar spine, a high percentage of morbidity and mortality is associated with cervical tuberculosis. Cervical tuberculosis accounts for about 10% of cases, with the major concerns being quadriparesis/quadriplegia and kyphotic deformity. Herein we describe our experience with the use of anterior instrumentation with titanium implants in 46 patients with subaxial tuberculosis. MATERIALS AND METHODS: Included in the study were a total of 46 patients with subaxial cervical (C3-C7) and upper dorsal (D1-D3) tuberculosis who underwent operations with anterior debridement, decompression, bone grafting, and anterior instrumentation by a single surgeon at our institute between January 2007 and December 2014. A review of the demographic data, medical records, and x-rays before and after surgery and at subsequent follow-ups was performed retrospectively from the departmental database. RESULTS: Neurological involvement in the postoperative period was seen in 29 of the 30 patients, 26 of whom showed complete neurological recovery. The Cobb angle at presentation ranged from 2°-58° of kyphosis with an average kyphosis of 15.4°. The average lordosis after surgery was found to be 17.5° (ie, a mean correction of 32.9°). CONCLUSIONS: Anterior instrumentation of subaxial cervical tuberculosis with titanium implants provides good correction of kyphosis and provides reasonable neurologic recovery in patients and ensures a long-lasting functional outcome. LEVEL OF EVIDENCE: 4.

Nanoparticle O-H Bond Dissociation Free Energies from Equilibrium Measurements of Cerium Oxide Colloids.

A novel equilibrium strategy for measuring the hydrogen atom affinity of colloidal metal oxide nanoparticles is presented. Reactions between oleate-capped cerium oxide nanoparticle colloids (nanoceria) and organic proton-coupled electron transfer (PCET) reagents are used as a model system. Nanoceria redox changes, or hydrogen loadings, and overall reaction stoichiometries were followed by both 1H NMR and X-ray absorption near-edge spectroscopies. These investigations revealed that, in many cases, reactions between nanoceria and PCET reagents reach equilibrium states with good mass balance. Each equilibrium state is a direct measure of the bond strength, or bond dissociation free energy (BDFE), between nanoceria and hydrogen. Further studies, including those with larger nanoceria, indicated that the relevant bond is a surface O-H. Thus, we have measured surface O-H BDFEs for nanoceria-the first experimental BDFEs for any nanoscale metal oxide. Remarkably, the measured CeO-H BDFEs span 13 kcal mol-1 (0.56 eV) with changes in the average redox state of the nanoceria colloid. Possible chemical models for this strong dependence are discussed. We propose that the tunability of ceria BDFEs may be important in explaining its effectiveness in catalysis. More generally, metal oxide BDFEs have been used as predictors of catalyst efficacy that, traditionally, have only been accessible by computational methods. These results provide important experimental benchmarks for metal oxide BDFEs and demonstrate that the concepts of molecular bond strength thermochemistry can be applied to nanoscale materials.

Are Hydroxyapatite-Coated Screws a Good Option for Sacroiliac Joint Stabilization? A Prospective Outcome Study.

OBJECTIVE: This is a single-surgeon series to prospectively evaluate the clinical and radiologic results of sacroiliac joint (SIJ) stabilization using hydroxyapatite (HA)-coated, fully threaded screws in patients with SIJ dysfunction. METHODS: A total number of 40 patients underwent percutaneous SIJ stabilization using HA-coated screws between 2013 and 2015 at the University Hospital of LLandough with an age range of 33-84 years. Patients were followed up closely, and outcome scores were collected preoperative and 12 months after surgery. Preoperative and postoperative outcomes were evaluated using patient-reported outcome measures (PROMs), Short Form-36, Oswestry Disability Index, EuroQol-5D-5L, and Majeed Pelvic Scores. RESULTS: Thirty-three patients (8 male and 32 female) out of the 40 patients completed follow-up. There was an overall improvement in all PROMs; however, only mental component of SF-36, Oswestry Disability Index, Majeed Pelvic Scores, and EuroQol-5D-5L were statistically significant. Twenty-one patients (63%) had lysis around the screw, and a subgroup analysis showed that improvement in PROMs was significantly less in patients with lysis around the screw. Four patients with lysis around the screw were offered revision due to ongoing pain. Revision was successful in only 1 patient. CONCLUSIONS: Percutaneous SIJ fixation procedure has been shown to have good clinical outcomes, but the use of HA-coated fully threaded screws in this procedure is not recommended on the basis of patient-reported outcome measures and radiologic findings in this prospective study.

A comparative review of 1,004 orthopaedic trauma patients before and during the COVID-19 pandemic.

AIMS: COVID-19 necessitated abrupt changes in trauma service delivery. We compare the demographics and outcomes of patients treated during lockdown to a matched period from 2019. Findings have important implications for service development. METHODS: A split-site service was introduced, with a COVID-19 free site treating the majority of trauma patients. Polytrauma, spinal, and paediatric trauma patients, plus COVID-19 confirmed or suspicious cases, were managed at another site. Prospective data on all trauma patients undergoing surgery at either site between 16 March 2020 and 31 May 2020 was collated and compared with retrospective review of the same period in 2019. Patient demographics, injury, surgical details, length of stay (LOS), COVID-19 status, and outcome were compared. RESULTS: There were 1,004 urgent orthopaedic trauma patients (604 in 2019; 400 in 2020). Significant reductions in time to theatre and LOS stay were observed. COVID-19 positive status was confirmed in 4.5% (n = 18). The COVID-19 mortality rate was 1.8% (n = 7). Day-case surgery comprised 47.8% (n = 191), none testing positive for COVID-19 or developing clinically significant COVID-19 symptoms requiring readmission, at a minimum of 17 days follow-up. CONCLUSION: The novel split-site service, segregating suspected or confirmed COVID-19 cases, minimized onward transmission and demonstrated improved outcomes regarding time to surgery and LOS, despite altered working patterns and additional constraints. Day-surgery pathways appear safe regarding COVID-19 transmission. Lessons learned require dissemination and should be sustained in preparation for a potential second wave or, the return of a "normal" non-COVID workload.Cite this article: Bone Joint Open 2020;1-9:568-575.

A comparative study looking at trauma and orthopaedic operating efficiency in the COVID-19 era.

BACKGROUD: COVID-19 has led to a reduction in operating efficiency. We aim to identify these inefficiencies and possible solutions as we begin to pursue a move to planned surgical care. METHODS: All trauma and orthopaedic emergency surgery were analysed for May 2019 and May 2020. Timing data was collated to look at the following: anaesthetic preparation time, anaesthetic time, surgical preparation time, surgical time, transfer to recovery time and turnaround time. Data for 2019 was collected retrospectively and data for 2020 was collected prospectively. RESULTS: A total of 222 patients underwent emergency orthopaedic surgery in May 2019 and 161 in May 2020. A statistically significant increase in all timings was demonstrated in 2020 apart from anaesthetic time which demonstrated a significant decrease. A subgroup analysis for hip fractures demonstrated a similar result. No increase in surgical time was observed in hand and wrist surgery or for debridement and washouts.Although the decrease in anaesthetic time is difficult to explain, this could be attributed to a reduction in combined anaesthetic techniques and possibly the effect of fear. The other increases in time demonstrated can largely be attributed to the PPE required for aerosol generating procedures and other measures taken to reduce spread of the virus. These procedures currently form a large amount of the orthopaedic case load. CONCLUSION: COVID-19 has led to significant reductions in operating room efficiency. This will have significant impact on waiting times. Increasing frequency of regional anaesthesia concurrently with non-aerosol generating surgeries may improve efficiency.

Determining Proton-Coupled Standard Potentials and X-H Bond Dissociation Free Energies in Nonaqueous Solvents Using Open-Circuit Potential Measurements.

Proton-coupled electron transfer (PCET) reactions are increasingly being studied in nonaqueous conditions, where the thermochemistry of PCET substrates is largely unknown. Herein, we report a method to obtain electrochemical standard potentials and calculate the corresponding bond dissociation free energies (BDFEs) of stable PCET reagents in nonaqueous solvents, using open-circuit potential (OCP) measurements. With this method, we measure PCET thermochemistry in acetonitrile and tetrahydrofuran for substrates with O-H and N-H bonds that undergo 1e-/1H+ and 2e-/2H+ redox processes. We also report corrected thermochemical values for the 1/2H2(g)/H•1M and H+/H• (CG) couples in several organic solvents. For 2e-/2H+ couples, OCP measurements provide the multielectron/multiproton standard potential and the average of the two X-H BDFEs. In contrast to traditional approaches for calculating BDFEs from electrochemical measurements, the OCP method directly measures the overall PCET reaction thermodynamics and avoids the need for a pKa scale in the solvent of interest. Consequently, the OCP approach yields more accurate thermochemical values and should be general to any solvent mixture compatible with electrochemical measurements. The longer time scale of OCP measurements enables accurate thermochemical measurements for redox couples with irreversible or distorted electrochemical responses by cyclic voltammetry, provided the PCET reaction is chemically reversible. Recommendations for successful OCP measurements and limitations of the approach are discussed, including the current inability to measure processes involving C-H bonds. As a straightforward and robust technique to determine nonaqueous PCET thermochemistry, these OCP measurements will be broadly valuable, with applications ranging from fundamental reactivity studies to device development.

Management dilemma of tuberculous paraplegia in pregnancy - A case report and review of literature.

BACKGROUND: Tuberculosis (TB)/tuberculous spondylodiscitis of the spine causing paraplegia in the 2nd trimester of pregnancy is rare and poses significant management dilemmas. Pregnancy, a relatively immunocompromised state with high hormonal levels, may prompt rapid TB destruction of a vertebral body resulting in an acute/ profound neurological deficit. Here, a pregnant paraplegic mother was diagnosed with spondylodiscitis that warranted immediate decompression/fusion to achieve neurological recovery. CASE DESCRIPTION: A 26-year-old female was 23 weeks pregnant when she presented with an acute spastic paraplegia (complete motor, sensory deficit, and sphincter loss). Operative decompression utilized a Versatile Approach along with a "Hartshill rectangle" for fusion and sublaminar wiring. This procedure accomplished simultaneous anterior and posterior fixation with a single approach without the need for intraoperative radiologic imaging. Although the pregnancy was continued with an uneventful perioperative period, intra-uterine fetal demise was documented 1 month postoperatively. Within 18 postoperative months the patient was neurologically intact, and fusion was confirmed on a computed tomography scan. CONCLUSION: A 23-week pregnant female acutely became paraplegic due to T5 tuberculous spondylitis confirmed on an X-ray (only source of radiation), and magnetic resonance imaging. Following a decompression/ instrumented fusion performed without fluoroscopic guidance, the patient regained full neurological function. However, 1 month postoperatively, the fetus spontaneously aborted.

Redox Reactivity of Colloidal Nanoceria and Use of Optical Spectra as an In Situ Monitor of Ce Oxidation States.

Nanoscale cerium oxide is of increasing interest in catalysis, biomedicine, renewable energy, and many other fields. Its versatility derives from the ability to form nonstoichiometric oxides that include both Ce3+ and Ce4+ ions. This work describes oxidation and reduction reactivity of colloidal cerium oxide nanocrystals, termed nanoceria, under very mild solution conditions. For instance, the as-prepared nanoceria oxidizes hydroquinone to benzoquinone, with reduction of some of the Ce4+ ions. Highly reduced nanoceria, prepared by UV irradiation in the presence of ethanol, oxidize hydroquinone back to benzoquinone. This and related reactivity allow tuning of the average cerium oxidation state in the nanocrystals without changes in size or other properties. The amounts of Ce3+ and Ce4+ in the nanoceria were determined both by X-ray absorption spectroscopy and from the stoichiometry of the reactions, measured using 1H NMR spectroscopy. The results demonstrate, for the first time, that the optical absorbance of nanoceria is linearly related to the percent Ce3+ in the sample. The decrease in absorption (blue-shift of the band edge) is due to increasing amounts of Ce3+, not to a quantum confinement effect. These findings demonstrate the facile solution reactivity of nanoceria and establish UV-visible spectroscopy as a powerful new tool for in situ determination of Ce oxidation states in ceria nanomaterials.