Photocatalytic Optical Hollow Fiber with Enhanced Visible-light-driven CO2 Reduction.

A visible-light-driven CO2 reduction optical fiber is fabricated using graphene-like nitrogen-doped composites and hollow quartz optical fibers to achieve enhanced activity, selectivity, and light utilization for CO2 photoreduction. The composites are synthesized from a lead-based metal-organic framework (TMOF-10-NH2 ) and g-C3 N4 nanosheet (CNNS) via electrostatic self-assembly. The TMOF-10-NH2 /g-C3 N4 (TMOF/CNNS) photocatalyst with an S-type heterojunction is coated on optical fiber. The TMOF/CNNS coating, which has a bandgap energy of 2.15 eV, has good photoinduced capability at the coating interfaces, high photogenerated electron-hole pair yield, and high charge transfer rate. The conduction band potential of the TMOF/CNNS coating is more negative than that for CO2 reduction. Moreover, TMOF facilitates the CO desorption on its surface, thereby improving the selectivity for CO production. High CO2 photoreduction and selectivity for CO production is demonstrated by the TMOF/CNNS-coated optical fiber with the cladding/core diameter of 2000/1000 µm, 10 wt% TMOF in CNNS, coating thickness of 25 µm, initial CO2 concentration of 90 vol%, and relative humidity of 88% RH under the excitation wavelength of 380-780 nm. Overall, the photocatalytic hollow optical fiber developed herein provides an effective and efficient approach for the enhancement of light utilization efficiency of photocatalysts and selective CO2 reduction.

Fiber optic sensor for nondestructive detection of microbial growth on a silk surface.

To nondestructively detect the mold growth process on silk, a coaxial concave reflection conical fiber optic sensor was developed using conical quartz fibers, fiber connectors, fiber couplers, and a plastic fixator. We established a theoretical model of this sensor and studied the influence of its structural parameters on its sensitivity, characterized the morphology of Aspergillus niger, and detected its growth process on a silk surface. A linear relationship between the sensor's output signal and the mold height was found. The sensor sensitivity, maximum detection error, and low limit of detection were 2.4 E-5 AU/µm, 7.83%, and 10 µm, respectively.

Monitoring Biohydrogen Production and Metabolic Heat in Biofilms by Fiber Bragg Grating Sensors.

A fiber Bragg grating (FBG) was created to accurately and simultaneously monitor the biohydrogen and metabolic heat production in biofilms containing Rhodopseudomonas palustris CQK-01 photosynthetic bacteria (PSB). The proposed hydrogen sensor was made from an FBG unit separated into two regions by a wet etching process; a thin region with a diameter of 15 µm was employed to monitor the temperature. A smaller region of the etched FBG with a diameter of 8.0 µm was coated with a 50 nm-thick Pd film by sputtering to determine the responses to the temperature and hydrogen concentration. To monitor the biohydrogen production and metabolic heat within the biofilms, three FBGs were evenly distributed in a polydimethylsiloxane channel (biofilm carrier) with vertical distances of 80 µm. In addition, the thickness, surface morphology, active biomass, and porosity of the biofilms were investigated. The FBG sensor can rapidly and accurately determine the difference in Bragg wavelength shifts caused by changes in the hydrogen concentration and temperature. The measured biohydrogen concentration is highly correlated with the real biohydrogen production with a correlation of 0.9765. The biohydrogen production capacity of PSB in the surface layer is much higher than that internally because of sharp decreases in the active biomass and porosity from the surface to within the biofilm. The highest biohydrogen concentration is obtained at 1.218 × 104 ppm for a biofilm thickness of 165 µm, and the temperature difference from metabolic heat production is ∼1.1 °C in the biofilm culture.

Monitoring Microalgal Biofilm Growth and Phenol Degradation with Fiber-Optic Sensors.

Simple D-type plastic optical fiber (POF) probes (i.e., sensor, reference, and photochemical probes) were created to accurately monitor the progression and phenol degradation of a Chlorella vulgaris biofilm. The sensor and reference probes were used to monitor the biofilm growth (thickness). The sensor probe, which consisted of a D-shaped POF and Canada balsam doped with GeO2 (CBG) coating, was developed to monitor the biofilm growth and change in the liquid-phase composition and its concentration inside the biofilm. The reference probe, which comprised a D-shaped POF, CBG coating, and glass fiber membrane (to separate the liquids from Chlorella vulgaris), was used to measure the response to changes in the liquid phase. A model was developed to demonstrate the accurate measurement of the biofilm thickness. The photochemical POF probe was coupled with a high-permselectivity phenol polymer membrane to monitor the phenol concentration and analyze the degradation time of 50 mg/L phenol with microalgal biofilms. A fixed relationship was obtained between the biofilm sensor output information and biofilm thickness for a biofilm thickness range of 0-290 µm with a periodic supply of 50 mg/L phenol solution. The highest phenol degradation rate occurred at a biofilm thickness of 191-222 µm. The proposed system can be used to investigate microalgal biomass and can provide a promising avenue for research on renewable resources and pollutant degradation.

Photochemical reflective optical fiber sensor for selective detection of phenol in aqueous solutions.

A photochemical fiber-optic sensor was developed by integrating a plastic optical fiber (POF), polymer membrane, gold mirror, and TiO2-based composite, and was shown to sensitively and selectively detect phenol in aqueous solution. The sensing element consisted of a thinned POF and visible-light-driven SiO2/N-doped TiO2 coating. The gold mirror was used to develop a reflective POF probe. The polymer membrane with high phenol permselectivity was employed to form a micro-channel between the membrane and probe. Our findings highlight the sensor's capability of phenol detection in aqueous solutions with high sensitivity of 0.294×10-3 (mg·L-1)-1, pH immunity ranging from 2.0 to 14.0, and high selectivity with a limit of detection of 30 µg·L-1.

Study on spectral and refractive index sensing characteristics of etched excessively tilted fiber gratings.

We investigated the spectral and refractive index (RI) sensing characteristics of the excessively tilted fiber grating (Ex-TFG) with different cladding diameters. The Ex-TFG is inscribed in standard single-mode fiber, and the cladding reduces from 125 µm to around 15 µm by the chemical etching method. Experimental results show that the number of cladding modes decreases, and the spacing of adjacent resonance peaks becomes larger and larger with the reduction of the cladding diameter in the observed wavelength range of 1250-1650 nm. The average RI sensitivity in the index region of 1.33-1.38, the one near 1.33, and the one at around 1.38 of the etched Ex-TFG with a diameter of 15 µm is ∼6.3, ∼5.3, and ∼6.67 fold compared to those of the no-etched Ex-TFG, respectively. Also, the RI sensing performances of the etched Ex-TFG with a diameter smaller than 30 µm are better than those of the Ex-TFG inscribed in SM1500 (4.2 µm/80 µm) fiber in the index region of 1.33. The proposed micronano Ex-TFG has higher RI sensitivity and a more compact structure in biosensing applications, compared to the standard Ex-TFGs and Ex-TFGs inscribed in SM1500 fiber.

Luminous exothermic hollow optical elements for enhancement of biofilm growth and activity.

In this work, we present a luminous-exothermic hollow optical element (LEHOE) that performs spectral beam splitting in the visible spectral range for the enhancement of biofilm growth and activity. The LEHOE is composed of a four-layer structure with a fiber core (air), cladding (SiO2), coating I (LaB6 film), and coating II (SiO2-Agarose-Medium film). To clarify the physical, optical and photothermal conversion properties of the LEHOE, we determined the surface morphology and composition of the coating materials, and examined the luminous intensity and heating rate at the LEHOE surface. The biofilm activity on the biocompatible LEHOE is far greater than that of commercial fibers, and the biofilm weight on the LEHOE is 4.5 × that of the uncoated hollow optical element.

Wet etching technique for fabrication of a high-quality plastic optical fiber sensor.

In this study, a simple wet etching technique is developed by employing aqueous solutions of acetic acid and ultrasonic irradiation for the fabrication of a high-quality plastic optical fiber (POF) sensor. The effects of acetic acid concentration and temperature and ultrasonic power on the etching rate and surface morphology of the etched POFs are investigated. The transmission spectrum and sensitivity of the etched POF sensors are evaluated using glucose solutions. We discovered that the POF sensors, which are fabricated using an aqueous solution of acetic acid with a concentration of 80 vol. % under an ultrasonic power of 130 W and temperature of 25°C, exhibit good light transmission and a high sensitivity of 9.10 [(RIU)(g/L)]-1 in the glucose solutions.

Effect of heat treatments on the performance of polymer optical fiber sensor.

Although the numerous advantages of polymer optical fiber (POF) sensors have been applied in different fields, the measurement consistency and sensitivity of POF evanescent wave (EW) sensors are still affected by its thermal stability and water absorption. Therefore, we perform a study to demonstrate the mechanism of the effect of heat treatments on physical and optical properties of POF EW sensors. We investigate the surface morphology, composition, refractive index, geometry, and weight of the fiber-sensing region subjected to water and vacuum heat treatments. We examine the spectral transmission and transmitted light intensity of POF sensors. We present a theoretical investigation of the effect of heat treatments on the sensitivity of POF EW sensors. The performance of the prepared sensor is evaluated using glucose and Chlorella pyrenoidosa analytes. We discovered that the spectral transmission and transmitted light intensity of the fibers shows little effect of vacuum heat treatments. In particular, the sensors, which subject to vacuum heat treatment at 110 °C for 3 h, exhibit temperature-independent measuring consistency and high sensitivity in glucose solutions in the temperature range 15-60 °C and also show high sensitivity in Chlorella pyrenoidosa solutions.

Fiber-optic differential absorption sensor for accurately monitoring biomass in a photobioreactor.

A fiber-optic differential absorption sensor was developed to accurately monitor biomass growth in a photobioreactor. The prepared sensor consists of two probes: the sensor and the reference. The sensor probe was employed to monitor the biomass and changes in the liquid-phase concentration in a culture. To separate the liquids from photosynthetic bacteria CQK 01 and measure the liquid-phase concentration, a proposed polyimide-silica hybrid membrane was coated on the sensing region of the reference probe. A linear relationship was observed between the sensor output signal and the biomass from the lag phase to the decline phase.

Fiber Bragg grating with polyimide-silica hybrid membrane for accurately monitoring cell growth and temperature in a photobioreactor.

A microstructured fiber Bragg grating (MSFBG) was created to accurately and simultaneously monitor the cell growth of photosynthetic bacteria (PSB) Rhodopseudomonas palustris CQK 01 and the temperature in a photobioreactor. The proposed sensor was made from an FBG unit that was separated into three regions, an unperturbed region, and two etched regions with smooth surfaces. The unperturbed grating region was employed to monitor the temperature. To eliminate the effects of the liquid concentration and temperature on the biomass, a polyimide-silica hybrid membrane was created and coated on an etched grating region to separate the liquids from the PSB; that is, this thinned region was developed to analyze the liquid concentration and temperature. Another etched grating region with a smaller diameter was used to determine the response to the temperature, biomass, and liquid concentration. In addition, two models were also presented to demonstrate accurate simultaneous measurement of the biomass and temperature. We discovered that the MSFBG sensor can rapidly and accurately determine the difference in the Bragg wavelength shifts caused by changes in the temperature, biomass, and liquid-phase concentration. The measured biomass is highly correlated with the real cell growth, with a correlation of 0.9438; the hydrogen production rate and temperature difference from metabolic heat production reached 1.97 mmol/L/h and 2.8 °C, respectively, in the PSB culture.

A fiber-optic sensor for accurately monitoring biofilm growth in a hydrogen production photobioreactor.

A new simple fiber-optic evanescent wave sensor was created to accurately monitor the growth and hydrogen production performance of biofilms. The proposed sensor consists of two probes (i.e., a sensor and reference probe), using the etched fibers with an appropriate surface roughness to improve its sensitivity. The sensor probe measures the biofilm growth and change of liquid-phase concentration inside the biofilm. The reference probe is coated with a hydrophilic polytetrafluoroethylene membrane to separate the liquids from photosynthetic bacteria Rhodopseudomonas palustris CQK 01 and to measure the liquid concentration. We also developed a model to demonstrate the accuracy of the measurement. The biofilm measurement was calibrated using an Olympus microscope. A linear relationship was obtained for the biofilm thickness range from 0 to 120 µm with a synthetic medium under continuous supply to the bioreactor. The highest level of hydrogen production rate occurred at a thickness of 115 µm.

Adsorption performance of Ni(II) by KOH-modified biochar derived from different microalgae species.

Microalgae biochar is potential adsorbents to remove heavy metals from wastewater due to abundant functional groups, high porosity and wide sources, but performance is not fully developed since it depends on microalgae species attributing to distinct morphology and biomass compositions. Here, two microalgae species Chlorella Pyrenoidosa and Scenedesmus Obliquus were used for biochar preparation via KOH-modification, biochar properties and their influences on Ni(II) adsorption were investigated. Ni(II) adsorption performances responding to biochar properties and operating conditions were upgraded via progressive optimization and response surface methodology. Together, adsorption isotherms and kinetics were analyzed to obtain significant factors for Ni(II) removal. As results, 100 % of Ni(II) removal was achieved under 100 mg/L initial Ni(II) concentration as pH was higher than the biochar zero-charge point of 6.87 with low biochar dosage (0.5 g/L), which provides an efficient approach for heavy metal removal from wastewater with microalgae biochar.

GeO2-SiO2-chitosan-medium-coated hollow optical fiber for cell immobilization.

A GeO(2)-SiO(2)-chitosan-medium (GSCM)-coated hollow optical fiber (HOF) is proposed. The HOF consists of three parts: the fiber core (air), cladding (SiO(2)), and coating (GSCM), which shows the highest refractive index of the three. The HOF's luminescence properties and surface morphology are investigated. Their adsorption capacity for Rhodopseudomonas palustris CQK 01 is also assayed. We discovered that when the amount of 2GeO(2)-SiO(2) sol dopant is 0.9 mass percent, the HOF exhibits the highest luminous intensity and uniform light distribution, and the adsorption capacity for the cell is 3.2 times higher than that of a normal solid optical fiber.

High-quality fiber fabrication in buffered hydrofluoric acid solution with ultrasonic agitation.

An etching method for preparing high-quality fiber-optic sensors using a buffered etchant with ultrasonic agitation is proposed. The effects of etching conditions on the etch rate and surface morphology of the etched fibers are investigated. The effect of surface roughness is discussed on the fibers' optical properties. Linear etching behavior and a smooth fiber surface can be repeatedly obtained by adjusting the ultrasonic power and etchant pH. The fibers' spectral quality is improved as the ratio of the pit depth to size decreases, and the fibers with smooth surfaces are more sensitive to a bacterial suspension than those with rough surfaces.

Effects of surface roughness on optical properties and sensitivity of fiber-optic evanescent wave sensors.

The effects of surface roughness on the light transmission properties and sensitivity of fiber-optic evanescent wave sensors are investigated. A simple method of increasing the sensitivity based on the surface roughness (pit depth δ and diameter Δ) and incident angle U(i) of light rays on the fiber input end is proposed. We discovered that as 2δ/Δ increases, the transmitted light intensity decreases, but the sensitivity initially increases and then decreases. In sensors containing fibers of various roughnesses, the sensitivity to glucose solutions reached -11.7 mW/riu at 2δ/Δ=0.32 and increased further to -15.3 mW/riu with proper adjustment of U(i).

Polyacrylate stabilized ZVI/Cu bimetallic nanoparticles for removal of hexavalent chromium from wastewater.

In this work, a magnetic core-shell composite zero-valent iron/copper-polyacrylate (ZVI/Cu-PAA) was synthesized by a simple liquid-phase reduction process and used for hexavalent chromium Cr(VI) removal from wastewater. The optimization experiments show that the optimal dosages of polyacrylate and Cu are 7.00 wt% and 8.25 wt%, respectively. The maximum adsorption capacity and removal rate of Cr(VI) by ZVI/Cu-PAA reached 106.12 mg g-1 and 99.05% at pH 5.5, respectively. Furthermore, the presence of coexisting ions such as Ca2+, Mg2+, Na+, and NO3- had no significant effect on its Cr(VI) removal performance. The excellent performance of ZVI/Cu-PAA is attributed to that the modification of polyacrylate can not only give more active sites but also inhibit agglomeration of nano-metallic particles, while Cu doping promotes the electron generation and transformation of Fe(III)/Fe(II) and Cu(II)/Cu(I) redox cycles. This makes ZVI/Cu-PAA has rich active sites and excellent stability, and has broad application prospects in the remediation of Cr (VI) polluted wastewater. The magnetic core-shell composite ZVI/Cu-PAA has excellent Cr (VI) removal performance because of its rich active sites and high electron transformation efficiency.

Comprehensive insights into antibiotic resistance gene migration in microalgal-bacterial consortia: Mechanisms, factors, and perspectives.

With the overuse of antibiotics, antibiotic resistance gene (ARG) prevalence is gradually increasing. ARGs are considered emerging contaminants that are broadly concentrated and dispersed in most aquatic environments. Recently, interest in microalgal-bacterial biotreatment of antibiotics has increased, as eukaryotes are not the primary target of antimicrobial drugs. Moreover, research has shown that microalgal-bacterial consortia can minimize the transmission of antibiotic resistance in the environment. Unfortunately, reviews surrounding the ARG migration mechanism in microalgal-bacterial consortia have not yet been performed. This review briefly introduces the migration of ARGs in aquatic environments. Additionally, an in-depth summary of horizontal gene transfer (HGT) between cyanobacteria and bacteria and from bacteria to eukaryotic microalgae is presented. Factors influencing gene transfer in microalgal-bacterial consortia are discussed systematically, including bacteriophage abundance, environmental conditions (temperature, pH, and nutrient availability), and other selective pressure conditions including nanomaterials, heavy metals, and pharmaceuticals and personal care products. Furthermore, considering that quorum sensing could be involved in DNA transformation by affecting secondary metabolites, current knowledge surrounding quorum sensing regulation of HGT of ARGs is summarized. In summary, this review gives valuable information to promote the development of practical and innovative techniques for ARG removal by microalgal-bacterial consortia.

Photocatalytic synergistic biofilms enhance tetracycline degradation and conversion.

Tetracyclines are refractory pollutants that cause persistent harm to the environment and human health. Therefore, it is urgently necessary to develop methods to promote the efficient degradation and conversion of tetracyclines in wastewater. This report proposes a photobiocatalytic synergistic system involving the coupling of GeO2/Zn-doped phosphotungstic acid hydrate/TiO2 (GeO2/Zn-HPW/TiO2)-loaded photocatalytic optical hollow fibers (POHFs) and an algal-bacterial biofilm. The GeO2/Zn-HPW/TiO2 photocatalyst exhibits a broad absorption edge extending to 1000 nm, as well as high-efficiency photoelectric conversion and electron transfer, which allow the GeO2/Zn-HPW/TiO2-coated POHFs to provide high light intensity to promote biofilm growth. The resulting high photocatalytic activity rapidly and stably reduces the toxicity and increases the biodegradability of tetracycline-containing wastewater. The biofilm enriched with Salinarimonas, Coelastrella sp., and Rhizobium, maintains its activity for the rapid photocatalytic degradation and biotransformation of intermediates to generate the O2 required for photocatalysis. Overall, the synergistic photocatalytic biofilm system developed herein provides an effective and efficient approach for the rapid degradation and conversion of water containing high concentrations of tetracycline.

Peroxymonosulfate activated by photocatalytic fuel cell with g-C3N4/BiOI/Ti photoanode to enhance rhodamine B degradation and electricity generation.

The development of traditional photocatalytic fuel cell (PFC) is severely hindered by poor visible-light response and limited reaction space. In this study, a visible-light responsive PFC with g-C3N4/BiOI/Ti photoanode was proposed and applied to activate peroxymonosulfate (PMS) to degrade rhodamine B. The degradation rate, maximum power density and maximum photocurrent density of the PMS/PFC system were respectively 95.39%, 103.87 µW cm-2 and 0.62 mA cm-2, which was respectively 1.28, 2.18, and 1.98 times that of PFC. The excellent performance is attributed to the production of more reactive oxygen species and the extension of the reaction space range after the activation of PMS. The activation pathway of PMS and charge transfer pathway of the photoanode were discussed in detail, and it was proposed that PMS was activated by Z-scheme heterojunction g-C3N4/BiOI/Ti photoanode.