Progress 07/01/23 to 07/31/23

Outputs
Target Audience:Pani Clean has actively been forming networks with community water systems, and private well owners in Iowa and Nebraska who are most affected by nitrate contamination. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Training activities included training of graduate students and research engineers with advanced manufacturing and engineering skills. The students and professionals were trained in semiconductor photoelectrochemical engineering and fluidized reactor design along with protocols for detecting nitrate and nitrate reduction products using diverse spectroscopic techniques. Professional development activities included participation in Social impact Venture school and winning social impact award. How have the results been disseminated to communities of interest?Participation in Social impact Venture school and winning social impact award. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Impact: Nitrate is currently the most prevalent groundwater pollutant in Northern America, primarily from agricultural activities and changing nitrogen input to the land surface. In the US, over 7 million Americans drink water from community water systems (CWS) that contain nitrate (NO3-) at concentrations exceeding the maximum contaminant level (MCL). The go-to technologies for nitrate treatment from CWSs produce highly concentrated nitrate brine residuals and are limited by expensive brine disposal and management options. Further, more than 35 million acres of sub-surface drained land exist in the US, and no technology has established a significant market share that removes nitrate from agricultural drainage. Based on the scale of nitrate contamination in community water systems and the growing need to reduce nitrogen load from tile drainage, the total addressable market for nitrate removal is sizable. The proposed technology generates no nitrate waste and can be powered entirely using renewable electricity and will be in a favorable position to compete with or replace existing nitrate treatment technologies Major Accomplishments: Objective 1. Synthesize water-dispersible semiconducting particles with multicomponent nanoscale inorganic coatings and demonstrate nitrate conversion and hypochlorite production under illumination using a batch reactor. Task 1: Synthesis of particulate photocatalytic heterostructures (PPHs). Two major components constituted proposed PPHs - semiconductors and catalysts. Accomplishments of integrating them as one single unit is described here. Semiconductors (light absorption unit): Two promising semiconducting particle core absorbers - one that absorbs UV and Visible spectrum (absorber 1) and the other that absorbs majorly in UV spectrum (absorber 2) - were succesfully synthesized or purchased. The morphology and crystalline structure werecharacterized using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). Catalysts (reaction site): A novel fluidized photochemical deposition process was developed to selectively deposit earth abundant catalysts in nanoparticulate form on thesemiconductor surfaces.Stabilization coating: Since the semiconducting light absorbers used were highly stable in chemical and photoelectrochemical environments at neutral pH waters, no stabilization coatings were needed to protect the semiconductor surface. Data Collected: Digital photographs and scanning electron microscopy images were carried out to determine the catalyst coatings on semiconducting particles. Task 2: Test synthesized PPHs for nitrate reduction and chloride oxidation in a batch reactor. In this Task, an in-house batch reactor with a closed gas circulation system for initial PPH screening was designed. The synthesized PPHs were suspended in 20 ml of 100 mg-NO3/l NaNO3 solution and continuously stirred. The suspensions were irradiated using UV or visible spectrum.From the nitrate conversion results, we successfully identified the PPH demonstrating the highest specific nitrate reduction rate. This downselected PPH was then used for fluidizied bed reactor studies. Data Collected:For batch reactor studies, nitrate reduction products were identified using a reflectometric method. This method is based on the intensity of reflected light by two reactive pads on test strips that change in color intensity based on the concentration of a specific substance Summary and Discussion of Results:Task 1 - Highly dispersed catalytic particles were obtained on semiconducting particles. Task 2 - Stable nitrate reduction performance was achieved in the presence of light. No nitrate reduction performance was achieved with no catalyst and under dark testing conditions. Objective 2. Investigate ate nitrate conversion mechanism of synthesized photocatalytic heterostructures using operando spectroscopy and optimize photocatalyst formulations based on the results. Task 3: Rapid screening of photocatalyst's activity and selectivity using in-operando Raman spectrometry. U. Houston team custom designed and built an advanced operando Raman characterization system for screening PPHs, which allowed the LED light to illuminate the sample from the top while the Raman excitation light is incident from the bottom . This configuration effectively prevented the interference between the two light beams. Using this system, the Raman spectrum was succesfully obtained to elucidate nitrate conversion mechanism. Data Collected:Raman spectroscopic data with and without light illumination was collected on the particles synthesized in Task 1. For all these experiments, the particles were suspended in nitrate solution. Summary and Discussion of Results:Successfully identified adsorbates and reaction intermediates for nitrate reduction reaction and the mechanism for nitrate reduction depended on semiconductor quality, catalyst loading and nitrate concentration. Objective 3. Construct a 0.1L fluidized bed reactor and test the PPHs for their nitrate conversion efficiency and durability for continuous conversion of nitrates in different feed water sources. Tasks 4 and 5: Design, construct, and test down selected PPHs in 0.1L fluidized bed reactors. In this Task, a lab-scale (0.1 L reactor volume) single-jacketed fluidized bed reactor for nitrate treatment was successfully designed and built. The downselected PPHs were then fluidized and tested for nitrate conversion. The particlesdemonstrated stable nitrate to nitrogen conversion efficiencies exceeding 95%, accomplishing the major deliverable for Phase 1 project. The downselected particles were also tested for different nitrate concentrations (16.66 - 166 mg/l NO3-N) and also in the presence of varying monovalent and divalent ions. Remarkably, the nitrate reduction performance was not affected in the presence of other cations and anions with particles demonstrating reproducible high nitrate conversion percentages (>95%). However, we did see decrease in nitrate reduction rates when the particles were subjected to repeated nitrate treatment cycles. This will be addressed during the Phase 2 project. Data Collected: Design and construction of a cylindrical fluidized bed reactor. Products obtained because of nitrate reduction reaction using ion chromatography and reflectometric method. Summary and Discussion of Results:The results using a cylindrical fluidized bed reactor showed greater than 90% conversion of nitrates to nitrogen. The total volume of water treated was 1 L. Nitrate reduction performance was tested for different nitrate concentrations and in the presence of various monovalend and divalent ions. For all experiments the particles demonstrated high nitrate conversion percentages. No reduction of nitrate was observed for semiconductor particles with no catalyst or under dark testing conditions. Decrease in nitrate reduction ratesover repeated cycles were observed and will be evaluated further in Phase 2. Key Outcomes: Successfully synthesized materials that utilize light produced using renewable electricity to convert nitrates in waters to benign and value-added products. Also developed fundamental scientific understanding of the proposed process which would enable further optimization and improvement of the overall technology.

Publications

Progress 07/01/22 to 07/25/23

Outputs
Target Audience:Pani Clean has actively been forming networks with community water systems, and private well owners in Iowa and Nebraska who are most affected by nitrate contamination. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Training activities included training of graduate students and research engineers with advanced manufacturing and engineering skills. The students and professionals were trained in semiconductor photoelectrochemical engineering and fluidized reactor design along with protocols for detecting nitrate and nitrate reduction products using diverse spectroscopic techniques. Professional development activities included participation in Social impact Venture school and winning social impact award. How have the results been disseminated to communities of interest?Participation in Social impact Venture school and winning social impact award. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Impact: Nitrate is currently the most prevalent groundwater pollutant in Northern America, primarily from agricultural activities and changing nitrogen input to the land surface. In the US, over 7 million Americans drink water from community water systems (CWS) that contain nitrate (NO3-) at concentrations exceeding the maximum contaminant level (MCL). The go-to technologies for nitrate treatment from CWSs produce highly concentrated nitrate brine residuals and are limited by expensive brine disposal and management options. Further, more than 35 million acres of sub-surface drained land exist in the US, and no technology has established a significant market share that removes nitrate from agricultural drainage. Based on the scale of nitrate contamination in community water systems and the growing need to reduce nitrogen load from tile drainage, the total addressable market for nitrate removal is sizable. The proposed technology generates no nitrate waste and can be powered entirely using renewable electricity and will be in a favorable position to compete with or replace existing nitrate treatment technologies. Major Accomplishments: Objective 1. Synthesize water-dispersible semiconducting particles with multicomponent nanoscale inorganic coatings and demonstrate nitrate conversion and hypochlorite production under illumination using a batch reactor. Task 1: Synthesis of particulate photocatalytic heterostructures (PPHs). Two major components constituted proposed PPHs - semiconductors and catalysts. Accomplishments of integrating them as one single unit is described here. Semiconductors (light absorption unit): Two promising semiconducting particle core absorbers - one that absorbs UV and Visible spectrum (absorber 1) and the other that absorbs majorly in UV spectrum (absorber 2) - were succesfully synthesized or purchased. The morphology and crystalline structure were characterized using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). Catalysts (reaction site): A novel fluidized photochemical deposition process was developed to selectively deposit earth abundant catalysts in nanoparticulate form on the semiconductor surfaces. Stabilization coating:Since the semiconducting light absorbers used were highly stable in chemical and photoelectrochemical environments at neutral pH waters, no stabilization coatings were needed to protect the semiconductor surface. Data Collected: Digital photographs and scanning electron microscopy images were carried out to determine the catalyst coatings on semiconducting particles Task 2: Test synthesized PPHs for nitrate reduction and chloride oxidation in a batch reactor. In this Task, an in-house batch reactor with a closed gas circulation system for initial PPH screening was designed. The synthesized PPHs were suspended in 20 ml of 100 mg-NO3 /l NaNO3 solution and continuously stirred. The suspensions were irradiated using UV or visible spectrum. From the nitrate conversion results, we successfully identified the PPH demonstrating the highest specific nitrate reduction rate. This downselected PPH was then used for fluidizied bed reactor studies. Data Collected: For batch reactor studies, nitrate reduction products were identified using a reflectometric method. This method is based on the intensity of reflected light by two reactive pads on test strips that change in color intensity based on the concentration of a specific substance Summary and Discussion of Results: Task 1 - Highly dispersed catalytic particles were obtained on semiconducting particles. Task 2 - Stable nitrate reduction performance was achieved in the presence of light. No nitrate reduction performance was achieved with no catalyst and under dark testing conditions. Objective 2. Investigate ate nitrate conversion mechanism of synthesized photocatalytic heterostructures using operando spectroscopy and optimize photocatalyst formulations based on the results. Task 3: Rapid screening of photocatalyst's activity and selectivity using in-operando Raman spectrometry. U. Houston team custom designed and built an advanced operando Raman characterization system for screening PPHs, which allowed the LED light to illuminate the sample from the top while the Raman excitation light is incident from the bottom . This configuration effectively prevented the interference between the two light beams. Using this system, the Raman spectrum was succesfully obtained to elucidate nitrate conversion mechanism. Data Collected: Raman spectroscopic data with and without light illumination was collected on the particles synthesized in Task 1. For all these experiments, the particles were suspended in nitrate solution. Summary and Discussion of Results: Successfully identified adsorbates and reaction intermediates for nitrate reduction reaction and the mechanism for nitrate reduction depended on semiconductor quality, catalyst loading and nitrate concentration. Objective 3. Construct a 0.1L fluidized bed reactor and test the PPHs for their nitrate conversion efficiency and durability for continuous conversion of nitrates in different feed water sources. Tasks 4 and 5: Design, construct, and test down selected PPHs in 0.1L fluidized bed reactors. In this Task, a lab-scale (0.1 L reactor volume) single-jacketed fluidized bed reactor for nitrate treatment was successfully designed and built. The downselected PPHs were then fluidized and tested for nitrate conversion. The particles demonstrated stable nitrate to nitrogen conversion efficiencies exceeding 95%, accomplishing the major deliverable for Phase 1 project. The downselected particles were also tested for different nitrate concentrations (16.66 - 166 mg/l NO3-N) and also in the presence of varying monovalent and divalent ions. Remarkably, the nitrate reduction performance was not affected in the presence of other cations and anions with particles demonstrating reproducible high nitrate conversion percentages (>95%). However, we did see decrease in nitrate reduction rates when the particles were subjected to repeated nitrate treatment cycles. This will be addressed during the Phase 2 project. Data Collected: Design and construction of a cylindrical fluidized bed reactor. Products obtained because of nitrate reduction reaction using ion chromatography and reflectometric method. Summary and Discussion of Results: The results using a cylindrical fluidized bed reactor showed greater than 90% conversion of nitrates to nitrogen. The total volume of water treated was 1 L. Nitrate reduction performance was tested for different nitrate concentrations and in the presence of various monovalend and divalent ions. For all experiments the particles demonstrated high nitrate conversion percentages. No reduction of nitrate was observed for semiconductor particles with no catalyst or under dark testing conditions. Decrease in nitrate reduction rates over repeated cycles were observed and will be evaluated further in Phase 2. Key Outcomes: Successfully synthesized materials that utilize light produced using renewable electricity to convert nitrates in waters to benign and value-added products. Also developed fundamental scientificunderstanding of the proposed process which would enable further optimization and improvement of the overall technology.

Publications

Progress 07/01/22 to 02/28/23

Outputs
Target Audience:Pani Clean has actively been forming networks with community water systems, and private well owners in Iowa who are most affected by the nitrate contamination. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Training activities included training of graduate students and research engineers with advanced manufacturing and engineering skills. Professional development activities included participation in Social impact Venture school and winning social impact award. How have the results been disseminated to communities of interest?Participation in Social impact Venture school and winning social impact award. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we will: (1) Evaluate nitrate reduction performance and chloride oxidation performance in the batch reactor as a function of light intensity and wavelength. (2) Successfully understand the nitrate conversion and hypochlorite production efficiency using in-situ Raman spectrometry and down-select the best materials for testing under continuous operation. (3) Benchmark optimized materials from Objectives 1 and 2 for nitrate conversion and hypochlorite production in fluidized bed reactors for different simulated nitrate concentrations, water composition, and TDS concentration.

Impacts
What was accomplished under these goals? Impact: Nitrate is currently the most prevalent groundwater pollutant in Northern America, primarily from agricultural activities and changing nitrogen input to the land surface. In the US, over 7 million Americans drink water from community water systems (CWS) that contain nitrate (NO3-) at concentrations exceeding the maximum contaminant level (MCL). The go-to technologies for nitrate treatment from CWSs produce highly concentrated nitrate brine residuals and are limited by expensive brine disposal and management options. Further, more than 35 million acres of sub-surface drained land exist in the US, and no technology has established a significant market share that removes nitrate from agricultural drainage. Based on the scale of nitrate contamination in community water systems and the growing need to reduce nitrogen load from tile drainage, the total addressable market for nitrate removal is sizable. The proposed technology generates no nitrate waste and can be powered entirely using renewable electricity and will be in a favorable position to compete with or replace existing nitrate treatment technologies. Objective 1.Synthesize water-dispersible semiconducting particles with multicomponent nanoscaleinorganiccoatings and demonstrate nitrate conversion and hypochlorite production under illumination using a batch reactor. Major activities completed and experiments conducted Task 1 -We developed a scalable route to synthesize semiconducting microparticles coated with nitrate reduction catalysts. The semiconducting particles on their own acted as chloride oxidation catalysts and were stable under testing conditions. This task was carried out by University of Iowa. Task 2 -We tested the performance and durability of photocatalytic heterostructures synthesized in Task 1 for nitrate conversion in model nitrate-rich waters. A 20-ml batch reactor was used for performance evaluation under illumination. We observed no degradation in nitrate treatment performance after 24 hrs. of continuous illumination. This task was carried out by Pani Clean. Data Collected Task 1 -Digital photographs and scanning electron microscopy images were carried out to determine the catalyst coatings on semiconducting particles. Task 2 -Photocurrent data for nitrate reduction as a function of applied potential was collected to understand the light vs dark effect on nitrate reduction performance. For batch reactor studies, nitrate reduction products were identified using a reflectometric method. This method is based on the intensity of reflected light by two reactive pads on test strips that change in color intensity based on the concentration of a specific substance Summary and Discussion of Results Task 1 -Highly dispersed catalytic particles were obtained on semiconducting particles. Task 2 -Stable nitrate reduction performance was achieved in the presence of light. No nitrate reduction performance was achieved with no catalyst and under dark testing conditions. Objective 2. Investigate ate nitrate conversion mechanism of synthesized photocatalytic heterostructures using operando spectroscopy and optimize photocatalyst formulations based on the results. Major activities completed and experiments conducted Task 3 - An in-house Raman spectroscopy was used to successfully identify adsorbates and reaction intermediates on photocatalyst surfaces (prepared in Task 1) upon illumination to determine the reaction mechanism and hence the product distribution ratio under different operation conditions. This task was carried out by the University of Houston. Data Collected Raman spectroscopic data with and without light illumination was collected on the particles synthesized in Task 1. For all these experiments, the particles were suspended in nitrate solution. Summary and Discussion of Results Successfully identified adsorbates and reaction intermediates for nitrate reduction reaction and the mechanism for nitrate reduction depended on semiconductor quality, catalyst loading and nitrate concentration. Objective 3. Construct a 0.1L fluidized bed reactor and test the PPHs for their nitrate conversion efficiency and durability for continuous conversion of nitrates in different feed water sources. Major activities completed and experiments conducted Task 4 - A lab-scale (0.1 L reactor volume) cylindrical fluidized bed reactor was constructed using U. Iowa glass shop for nitrate treatment. Task 5 - We performed a preliminary assessment of the photocatalysts synthesized from Task 1 in the reactor developed in Task 4 for nitrate conversion. Tasks 4 and 5 were carried out by Pani Clean. Data Collected Task 4 - Design and construction of a cylindrical fluidized bed reactor. Task 5 - Products obtained because of nitrate reduction reaction using a reflectometric method. Summary and Discussion of Results The preliminary results using a cylindrical fluidized bed reactor showed promise, with semiconductor particles coated with catalysts showing a drop in nitrate concentration from 100 mg/l to <20 mg/l after 20 hours of illumination. The total volume of water treated was 1 L. No reduction of nitrate was observed for semiconductor particles with no catalyst or under dark testing conditions. Key outcomes: Successfully synthesized materials that utilize light produced using renewable electricity to convert nitrates in waters to benign and value-added products. Also developed fundamental scientific understanding of the proposed process which would enable further optimization and improvement of the overall technology.

Publications