Kenneth R. Davey

2D phosphorene as a water splitting photocatalyst: fundamentals to applications

Hydrogen from direct splitting of water molecules using photons is reckoned to be a sustainable and renewable energy solution for the post fossil-fuel era. Efficient photocatalysts, including metal-free photocatalysts, are key determinants of cost-effective hydrogen generation at a large-scale. The search for new materials that are metal-free is therefore ongoing. Recently, 2D phosphorene, a phosphorus analogue of graphene, has been added as a new semiconductor to the family of monolayer-flatland materials. In this review, we focus on analysing the fundamental electronic, optical and chemical properties of 2D phosphorene and assess its suitability as a metal-free water splitting photocatalyst. We also critically analyse its stability against claims from environmental antagonists and attempt to predict its future as a photocatalyst. This review provides timely information for researchers, scientists and professionals devoted to materials research for photocatalysis.

Thermal inactivation of bacteria-a new predictive model for the combined effect of three environmental factors: temperature, pH and water activity

Abstract An empirical, linear-Arrhenius model for predicting the combined effect of three environmental factors on the thermal inactivation (i.e. death) rate of Escherichia coli, namely inactivation temperature, pH and water activity (aw), is synthesised from published, and independent experimental data. For inactivation rates obtained both at isothermic condition, a constant temperature of 58 °C, with a seven level pH range (pH 3 to pH 9), and a three level range of values of aw (0.928 to 0.995); and anisothermic conditions (a range of inactivation temperature 52.05 to 63.10 °C, with a four level pH range of between pH 3 to pH 9, and a three level range of aw from 0.928 to 0.995), the model gave a very high degree of fit. The synthesised model is quadratic in form. For isothermic inactivation the model has three terms (pH, pH2, and aw2) and explained 96.7% of the variance accounted for (%V) in the overall data (i.e. seven levels of pH and three levels of aw). The model with four terms (l/T, pH, pH2, and aw2) explained 80.7% V in the overall anisothermic data, and between 90.1 and 95.3%V at each level of aw. Comparison with an existing model highlighted the advantages of the newly synthesised model including ease of formulation, and ease of use. The new model form should permit ready integration with equations describing the viscous and thermal properties in design for batch or continuous steriliser design. Findings suggest an additive linear-Arrhenius model is applicable to the combined influence of n environmental factors on the thermal inactivation rate.

Promotion of Electrocatalytic Hydrogen Evolution Reaction on Nitrogen-Doped Carbon Nanosheets with Secondary Heteroatoms

Dual heteroatom-doped carbon materials are efficient electrocatalysts via a synergistic effect. With nitrogen as the primary dopant, boron, sulfur, and phosphorus can be used as secondary elements for co-doped carbons. However, evaluation and analysis of the promotional effect of B, P, and S to N-doped carbons has not been widely researched. Here we report a robust platform that is constructed through polydopamine to prepare N,B-, N,P-, and N,S-co-doped carbon nanosheets, characterized by similar N species content and efficient B, P, and S doping. Systematic investigation reveals S to have the greatest promotional effect in hydrogen evolution reactions (HER) followed by P and that B decreases the activity of N-doped carbons. Experimental and theoretical analyses show the secondary heteroatom promotional effect is impacted by the intrinsic structures and extrinsic surface areas of both materials, i.e., electronic structures exclusively determine the catalytic activity of active sites, while large surface areas optimize apparent HER performance.

Linear-Arrhenius models for bacterial growth and death and vitamin denaturations

SummaryThe development of the quantitative, linear-Arrhenius model of Davey for predicting bacterial growth and death (inactivation) is reviewed. The applicability of the model to published data from independent researchers for both the growth phase and lag phase, involving combined environmental factors (T, aw) is illustrated. Also illustrated is its applicability to thermal inactivation kinetics and vitamin denaturation (with combinedT, pH). Integration of the model to produce complex models describing the thermal sterilization of liquid is demonstrated. Advantages of the model, including its simplicity and the fact that the coefficients to build the model can be obtained easily by relatively unsophisticated users, are highlighted in a comparison with other models.

Strongly Coupled Nafion Molecules and Ordered Porous CdS Networks for Enhanced Visible-Light Photoelectrochemical Hydrogen Evolution

Strongly coupled Nafion molecules and ordered porous CdS networks are fabricated for visible-light photoelectrochemical (PEC) hydrogen evolution. The Nafion layer coating shifts the band position of CdS upward and accelerates charge transfer in the photoelectrode/electrolyte interface. It is highly expected that the strong coupling effect between organic and inorganic materials will provide new routes to advance PEC water splitting.

Modelling the combined effect of temperature and pH on the rate coefficient for bacterial growth

An extension of a model of Davey (1989a) has been used to model data of Adams et al. (1991) describing the combined effect of temperature and pH on the rate coefficient for growth of Yersinia enterocolitica in liquid media acidified with four different acidulants: sulphuric, citric, lactic and acetic acids. The model explained between 97.8% and 99.1% of the variance in the results. This very good fit between the predictions and the observed data confirms pH can be incorporated into a model that had previously been applied to the combined effect of temperature and water activity, and to the effect of temperature alone. These findings, taken together with previously reported results, demonstrate the value of the model for predicting the combined effect of two environmental factors on the growth rate. Based on results reported in this paper and previously reported results, a generalised model is proposed for the combined effect of three or more environmental factors, that is amenable to testing.

Validation of a model for predicting the combined effect of three environmental factors on both exponential and lag phases of bacterial growth: temperature, salt concentration and pH

Abstract A linear-Arrhenius predictive model, hypothesised previously, for the combined effect of three or more environmental factors on bacterial growth was assessed against 66 growth curves of Salmonella spp. as effected by temperature (283–303 K), sodium chloride concentration (0.7–4.56% wt v ) and pH (5.63–6.77) for both the exponential (growth) phase and lag phase of growth. Lag times were determined by both traditional (subjective) microbiological methods and by the use of the Modified Gompertz equation. No significant difference (P ≤ 0.05) was found between values of the lag time determined by either of these two methods. Model predictions gave a very high degree of fit to these data explaining 97-6% of the per cent variance accounted for (%V) between observed and predicted values for the growth phase, and 94-6% V for the lag phase. The quadratic form of the model involves six terms to account for the three environmental factors: 1 T , 1 T 2 , salt, salt2, pH, pH2. These findings appear to confirm the generalised additive model proposed earlier (Davey, 1994). Advantages of the model include its accurate prediction of rate coefficient for growth and the duration of the lag time, parsimony (small number of coefficients) and ease of formulation and of use.

Activated sludge treatment of abattoir wastewater—I: Influence of sludge age and feeding pattern

Abstract As part of a study to provide data for the design of abattoir activated sludge plants laboratory-scale completely mixed reactors were fed with abattoir wastewater, continuously and intermittently using an 8 h feed, 16 h starvation pattern. The standard biokinetic coefficients and the effluent concentrations of COD. TKN and phosphorus were measured for the continuously fed reactors at sludge ages of 5, 10 and 20 days. Sludge settleability and filterability were also measured. Values obtained for the biokinetic coefficients Y and k d were within the range of values reported for other substrates but k was lower and k x higher. Effluent TKN and phosphorus concentrations were low at the three sludge ages, but the COD concentration was high at sludge ages of 5 and 10 days. In contrast to the data reported for many other wastewaters the effect of sludge age on the SVI was small. Intermittent feeding was tested at a single sludge age of 10 days. It produced an effluent and sludge with better and more stable characteristics than those from the continuously fed reactor at the same sludge age.

Thermal inactivation kinetics of three vegetative bacteria as influenced by combined temperature and pH in a liquid medium

The kinetics of thermal inactivation as affected by combined temperature and liquid pH for three vegetative bacteria— Escherichia coli (ATCC 25922), Listeria monocytogenes (SLCC 5764) and Pseudomonas fluorescens (172)— have been studied using published bench-scale data and additional experimentally determined data from the heating of samples in ampoules of thin-walled glass. These bacteria represent common micro-organisms known to grow in solid and liquid foods. Up to six levels of temperature (52, 54, 56, 58, 60 and 62° C) in combination with up to eight levels of pH (4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0 and 7.5) with exposure times ranging from 10 seconds to five minutes, were used in experimental designs to cover the wide biokinetic range of interest. The carrier liquid, a 2 kg m −3 mucilage of Carbopol ® 934 was selected because of the stability of its viscosity over the range of temperature and pH values, and its resistance to bacterial growth. The viscosity of this mucilage closely simulates that of a range of liquid foods. The effect of pH on the rate of thermal inactivation was significant for all three bacteria, especially at the lower exposure temperatures. However, because survivor data showed tailing with longer exposure times, the widely held assumption of first-order kinetics for thermal inactivation of vegetative bacteria is not supported. Concave-up tails appear in the data for P. fluorescens and E. coli and both concave-up and concave-down tails appear in the data for L. monocytogenes . Taken together, data for all three bacteria support the necessity for a model formulation for non-linear survivor kinetics as influenced by combined exposure temperature and liquid pH.

A Comparison of Predictive Models for the Combined Effect of UV Dose and Solids Concentration on Disinfection Kinetics of Escherichia Coli for Potable Water Production

A present lack of a rigorous quantitative understanding of the kinetics of ultraviolet (UV) inactivation of bacterial contaminants is shown to limit wide application and optimization of UV disinfection efficacy in the provision of potable water and treatment of wastewaters. Four appropriate mathematical model forms were synthesized from extensive published data for UV disinfection of Escherichia coli in reverse osmosis (RO) water with the addition of either a shielding agent or an absorbing agent and evaluated in a comparative study. Celite 503*** (with a median particle size of 23 μm) in suspended solids concentrations in the range 0.0 to 0.3 g l −1 was the UV shielding agent, and powdered coffee (International Roast***) concentrations in the range 0.0 to 0.03 g l −1 was the UV absorbing agent. The models were the classical log-linear, Davey linear-Arrhenius, Ratkowsky- Belehradek or square-root and a third order polynomial model ( n OP). The test criteria for model selection and ranking included goodness of fit and accuracy in prediction; relative complexity (i.e., parsimony ); ease of synthesis and use; and potential for physiological interpretation. The percent variance accounted for (%V ) in prediction was used as a stringent test of goodness of fit. The Davey linear-Arrhenius model explained an overall mean of 97.2% V . This compared with, respectively, 95.6, 93.0 and 86.7% V for the n OP, log-linear and square-root models. The poorer fit of the square-root model suggests that suspended solids concentration and UV dose act independently on disinfection kinetics as implied in the Davey linear-Arrhenius model. This model is quadratic in UV dose and linear in suspended solids concentration. It has three terms: [ dose ]., [ dose ]. 2 and [ conc ]. It best explained deviation in tailing from classically implied log-linear survivor kinetics for the rate of UV disinfection of viable bacterial cells. Overall it best fulfilled the criteria for model selection. Further, from a practical view, it is of a form that is readily integrated with equations describing the rheology and hydrodynamics of liquid flow that permit a simulation of a UV disinfection unit operation for the provision of potable water.