Solar remediation of wastewater and saline water with concurrent production of value-added chemicals

doi:10.1016/j.jece.2021.106919

Journal of Environmental Chemical Engineering

Volume 10, Issue 1, February 2022, 106919

https://doi.org/10.1016/j.jece.2021.106919 Get rights and content

Highlights

•
The photoconversion efficiency is a top priority assuming a ceaseless supply of treated water.
•
Producing treated water is energy-intensive and carbon-footprinted.
•
This article introduces solar splitting systems with contaminated water and saline water.
•
The solar splitting systems are classified into photocatalysis, photoelectrocatalysis, and PV-assisted electrocatalysis.
•
Hybrid devices working in wastewater and saline water are examined.

Abstract

Significant efforts have been undertaken to develop high-efficiency photoconversion materials and devices for the decentralized in situ production of carbon-neutral chemicals. Notably, photoconversion efficiency is a top priority assuming a ceaseless supply of artificially well-defined water. However, the production of treated water using existing processes is energy-intensive and generates a high carbon footprint. For the practical application of photoconversion systems, the use of untreated water is inevitable. Many organic and inorganic substrates present in untreated water actively participate in the production process of value-added chemicals and interfere with proton–electron transfer kinetics and mechanisms. From this perspective, solar splitting systems with contaminated water and saline water are introduced and the photoconversion systems are classified into photocatalysis, photoelectrocatalysis, and photovoltaic-assisted electrocatalysis. The oxidation and reduction reactions are separately discussed for each system, and hybrid devices developed for treating wastewater and saline water are examined in terms of their mechanism and efficiency.

Graphical Abstract

Section snippets

Sun-water-energy nexus

Over the past five decades, solar conversion technologies have received growing attention as an environmental-friendly and carbon–neutral process for producing value-added chemicals (H₂, carbon chemicals, and hydrogen peroxide) in aqueous systems [1], [2], [3], [4]. The solar potential is excellent. The standard terrestrial sunlight (air mass 1.5 G, 1 kW m⁻²) can generate an average daily power of ~250 W m⁻² yearly [5]. With this power density, a solar conversion process with 10% efficiency

Solar conversion systems

Three primary solar conversion systems have been developed so far for oxidizing water and producing value-added chemicals: photocatalysis (PC), photoelectrocatalysis (PEC), and photovoltaic-assisted electrocatalysis (PV-EC) (Fig. 1). This classification is rather arbitrary because various versions of hybrid systems have been reported. The uniqueness and relative features of the systems were compared and discussed elsewhere in detail [1], [3], [4], [7], [13] and this article briefly introduces

Production of reactive oxygen species for wastewater oxidation

The primary feature in solar wastewater splitting is production of single or many different reactive oxygen species (ROSs), such as hydroxyl radical (OH^•), superoxide anion radical (O₂^•−), hydroperoxyl radical (HOO^•), and ozone (O₃). Most ROSs are quickly transformed into one another (Figs. 2a and 2b) [65]. The aqueous (in)organic substrates are also oxidized via direct inner-sphere charge transfer. However, the direct charge transfer usually proceeds only for strongly adsorbed substrates

Solar treatment of saline water

Chloride is one of the most abundant, ubiquitous inorganic ions in most water types. Its concentration is ~0.3 mM in unpolluted water, 1 mM in rivers, ~5 mM in agricultural and contaminated water, 10–100 mM in brackish water, ~0.5 mM in seawater, and > 0.5 mM in brine water. Besides, wastewater contains a large amount of chloride (maximum ~30 mM in dairy wastewater, ~450 mM in textile wastewater, and 20–40 mM in human urine) [24]. Accordingly, the effects and use of chloride in treating

Summary

This article introduced the solar splitting of wastewater and saline water and classified them into PC, PEC, and PV-EC systems. For each system, the oxidation reactions (generation of ROSs and RCSs) and reduction reactions (HER, HPR, and CO₂RR) were separately discussed and their coupled reactions were examined for mechanisms and efficiency. Despite the same configuration, the wastewater and saline water splitting systems further consider the effect of (in)organic substrates in redox reactions.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was supported by the National Research Foundation (NRF-2018R1A6A1A03024962, NRF-2019R1A2C2002602, NRF-2021M3I3A1082880, and NRF-2021K1A4A7A02102598).

References (149)

K. Maeda et al.
Effect of electrolyte addition on activity of (Ga1−xZnx)(N1−xOx) photocatalyst for overall water splitting under visible light
Catal. Today
(2009)
J. Kim et al.
Electrolysis of urea and urine for solar hydrogen
Catal. Today
(2013)
N.C. Deb Nath et al.
Stand-alone photoconversion of carbon dioxide on copper oxide wire arrays powered by tungsten trioxide/dye-sensitized solar cell dual absorbers
Nano Energy
(2016)
H. Park et al.
Surface modification of TiO2 photocatalyst for environmental applications
J. Photochem. Photobiol., C.
(2013)
K. Kondo et al.
Development of highly efficient sulfur-doped TiO2 photocatalysts hybridized with graphitic carbon nitride
Appl. Catal. B
(2013)
U. Kang et al.
Lithium ion-inserted TiO2 nanotube array photoelectrocatalysts
Appl. Catal. B
(2013)
T.H. Jeon et al.
Ultra-efficient and durable photoelectrochemical water oxidation using elaborately designed hematite nanorod arrays
Nano Energy
(2017)
S.K. Choi et al.
Highly efficient hydrogen production using p-Si wire arrays and NiMoZn heterojunction photocathodes
Appl. Catal., B
(2017)
J.M. Jaksic et al.
Kinetic analysis of hydrogen evolution at Ni–Mo alloy electrodes
Electrochim. Acta
(2000)
S. Kim et al.
Reduced titania nanorods and Ni-Mo-S catalysts for photoelectrocatalytic water treatment and hydrogen production coupled with desalination
Appl. Catal. B
(2021)

W. Choi et al.

Electrocatalytic arsenic oxidation in bicarbonate solutions combined with CO₂ reduction to formate

Appl. Catal. B

(2020)

G. Kim et al.

Charge-transfer surface complex of EDTA-TiO(2) and its effect on photocatalysis under visible light

Appl. Catal. B

(2010)

Y.-C. Oh et al.

Photocatalytic degradation of a cyanuric acid, a recalcitrant species

J. Photochem. Photobiol. A

(2004)

S. Kim et al.

Selective charge transfer to dioxygen on KPF6-modified carbon nitride for photocatalytic synthesis of H2O2 under visible light

J. Catal.

(2018)

Y. Hori et al.

Electrocatalytic process of CO selectivity in electrochemical reduction of CO₂ at metal-electrodes in aqueous-media

Electrochim. Acta

(1994)

H. Park et al.

Photocatalytic conversion of carbon dioxide to methane on TiO2/CdS in aqueous isopropanol solution

Catal. Today

(2016)

S.Y. Choi et al.

Standalone photoconversion of CO₂ using Ti and TiOx-sandwiched heterojunction photocatalyst of CuO and CuFeO2

Appl. Catal. B

(2021)

S.H. Yoon et al.

Computational density functional theory study on the selective conversion of CO₂ to formate on homogeneously and heterogeneously mixed CuFeO2 and CuO surfaces

Catal. Today

(2019)

S.H. Yoon et al.

Theoretical insight into effect of cation-anion pairs on CO₂ reduction on bismuth electrocatalyst

Appl. Surf. Sci.

(2020)

M.G. Walter et al.

Solar water splitting cells

Chem. Rev.

(2010)

J. He et al.

Recent advances in solar-driven carbon dioxide conversion: expectations versus reality

ACS Energy Lett.

(2020)

J. Ronge et al.

Monolithic cells for solar fuels

Chem. Soc. Rev.

(2014)

A.J. Bard et al.

Artificial photosynthesis: solar splitting of water to hydrogen and oxygen

Acc. Chem. Res.

(1995)

B.A. Pinaud et al.

Technical and economic feasibility of centralized facilities for solar hydrogen production via photocatalysis and photoelectrochemistry

Energy Environ. Sci.

(2013)

M.R. Shaner et al.

A comparative technoeconmic analysis of renewable hydrogen production using solar energy

Energy Environ. Sci.

(2016)

J. Ivy

Summary of electrolytic hydrogen production: milestone completion report, National Renewable Energy

Lab. (NREL/MP-

(2004)

M. Jouny et al.

General techno-economic analysis of CO₂ electrolysis systems

Ind. Eng. Chem. Res.

(2018)

B.A. Parkinson

Advantages of solar hydrogen compared to direct carbon dioxide reduction for solar fuel production

ACS Energy Lett.

(2016)

F.E. Osterloh

The low concentration of CO₂ in the atmosphere is an obstacle to a sustainable artificial photosynthesis fuel cycle based on carbon

ACS Energy Lett.

(2016)

J. Liu et al.

Hydrogen peroxide production from solar water oxidation

ACS Energy Lett.

(2019)

K. Maeda et al.

Photocatalytic water splitting: recent progress and future challenges

J. Phys. Chem. Lett.

(2010)

R. Lal

Sequestration of atmospheric CO₂ in global carbon pools

Energy Environ. Sci.

(2008)

P.L. McCarty et al.

Domestic wastewater treatment as a net energy producer - Can this be achieved?

Environ. Sci. Technol.

(2011)

R. Esselman, The Carbon Footprint of Domestic Water Use in the Huron River Watershed, June...

The National Association of Clean Water Agencies Cost of Clean Water Index, available at...

M. Elimelech et al.

The future of sewater desalination: energy, technology, and the environment

Science

(2011)

D.F. Putnam, Composition and concentrative properties of human urine, NASA contractor report (NASA CR-1802), July,...

W. Xu et al.

Urea-based fuel cells and electrocatalysts for urea oxidation

Energy Technol.

(2016)

A.N. Rollinson et al.

Urea as a hydrogen carrier: a perspective on its potential for safe, sustainable and long-term energy supply

Energy Environ. Sci.

(2011)

X. Hu et al.

Urea electroxidation: current development and understanding of Ni-based catalysts

ChemElectroChem

(2020)

K. Ye et al.

Recend adances in the electro-oxidation of urea for direct urea fuel cell and urea electrolysis

V. Lazarova et al.

Water-Energy Interactions in Water Reuse

(2012)

J. Brillet et al.

Highly efficient water splitting by a dual-absorber tandem cell

Nat. Photonics

(2012)

T. Arai et al.

A monolithic device for CO₂ photoreduction to generate liquid organic substances in a single-compartment reactor

Energy Environ. Sci.

(2015)

S.Y. Reece et al.

Wireless solar water splitting using silicon-based semiconductors and earth-abundant catalysts

Science

(2011)

M.R. Hoffmann et al.

Environmental applications of semiconductor photocatalysis

Chem. Rev.

(1995)

H. Park et al.

Photoinduced charge transfer processes in solar photocatalysis based on modified TiO2

Energy Environ. Sci.

(2016)

H. Park

Interfacial charge transfers of surface-modified TiO2 nanoparticles in photocatalytic water treatment

S.U.M. Khan et al.

Efficient photochemical water splitting by a chemically modified n-TiO2

Science

(2002)

S. Kim et al.

Visible light active platinum-ion-doped TiO2 photocatalyst

J. Phys. Chem. B

(2005)

Cited by (14)

Advancement in solar energy-based technologies for sustainable treatment of textile wastewater: Reuse, recovery and current perspectives
2023, Journal of Water Process Engineering
The textile industry is categorized as the most energy-intensive and polluting industry in the world, where the wastewater treatment process presents significant environmental challenges. This review paper explores solar energy-based technologies used for treating textile wastewater addressing important questions regarding the mechanism of different solar technologies employed in textile wastewater treatment, the significance of solar-based approaches, and various solar technologies investigated in this field. The paper thoroughly discusses key elements such as the characterization of textile wastewater, involved processes, and contaminants released during each process. The findings indicate that solar energy-based technologies offer the advantage of utilizing renewable resources while promoting sustainability. Solar photocatalysis has proven effective in degrading a wider range of contaminants found in textile wastewater. The feasibility of this can be enhanced by synthesizing a new photocatalyst with a wider band gap and improved reusability and recyclability. Photovoltaic electrocoagulation and solar photoelectrocatalysis have demonstrated faster pollutant degradation and reduced sludge generation, along with the production of hydrogen gas. Microalgal bioremediation shows promising results for textile wastewater treatment, focusing on recovering various products and algal biomass. These technologies represent a future-oriented and sustainable approach to maximizing resource recovery while minimizing environmental impact. Strengths, weaknesses, opportunities, and threats (SWOT) analysis revealed these technologies to be efficient, an emerging need of the current era but are still developing with major operational challenges in rainy and local weather conditions. The bibliometric analysis is also being carried out for a better understanding of the textile wastewater treatment scenario.
Membraneless unbuffered seawater electrolysis for pure hydrogen production using PtRuTiO<inf>x</inf> anode and MnO<inf>x</inf> cathode pairs
2023, Applied Catalysis B: Environmental
Citation Excerpt :
Electrolytic hydrogen production is considered a key energy transition, carbon-neutral technology when coupled with renewable energy production processes [1–9].
Seawater electrolysis is promising as an in situ H₂ production method, allowing immediate overseas transport of the produced H₂. In this study, membraneless electrolysis of undisturbed, unbuffered seawater (pH 8.2) is proposed to produce high-purity H₂. A ternary Pt, Ru, and Ti (PRT) catalyst with a minimized Pt level (Pt_0.06Ru_0.24Ti_0.7O_x) drives chloride oxidation reaction (ClOR) at a Faradaic efficiency (FE) of ∼100% in saline water at current density (J) of 800 mA cm⁻² over 500 h. Chlorine reduction reaction (ClRR) is also inhibited on MnO_x electrodes, leading to hydrogen evolution reaction (HER) at an FE of ∼100% even in the presence of chlorine species (HClO/ClO⁻). Finally, the PRT anode/MnO_x cathode pair is demonstrated to drives ClOR and HER at FEs of ∼100% at J = 80 mA cm⁻² over 100 h in a single-compartment cell containing seawater. Oxygen evolution reaction and ClRR are completely inhibited during seawater electrolysis.
In-situ desalination-coupled electrolysis with concurrent one-step-synthesis of value-added chemicals
2023, Desalination
An efficient multi-functional electrolyzer with a Ni- and Fe-layered double hydroxide (NiFe-LDH) anode and a binary NiMo cathode is designed for overall water splitting coupled with the desalination of saline water and production of value-added chemicals. The NiFe-LDH and NiMo pairs separated by a bipolar membrane (BPM) show overpotentials as low as those of noble metal catalysts for oxygen and hydrogen evolution reactions in 1 M KOH and 1 M H₂SO₄ solutions, respectively. Arraying anion and cation-exchange membranes (AEMs and CEMs, respectively) with BPMs (NiFe-LDH/BPM/[AEM/CEM]_n/BPM/NiMo; n = 1 or 5) further enables the desalination of brackish water and seawater at specific energy consumption of 1.8 kWh m⁻³, with concurrent production of HCl and NaOH. The Faradaic efficiencies of the device for O₂ and H₂ production are >95 % at J = 100 mA cm⁻² over 20 h, while the initial pH values of the anolyte and catholyte remain unchanged. Detailed surface characterization of the electrocatalysts is performed, and various electrolyzer configurations are compared in terms of desalination efficiency.
Photoelectrochemical behaviors and photocatalytic activities of mixed CuO and CuFeO<inf>2</inf> films with Ti and Ni underlayers for CO<inf>2</inf> conversion
2023, Applied Catalysis A: General
This study synthesizes heterojunction CuO and CuFeO₂ (CFO) films via electrodeposition on Ti and Ni-deposited transparent conducting substrates and examines their photoelectrochemical behavior and unassisted photocatalytic activities for CO₂ conversion in aqueous bicarbonate solutions at circumneutral pH. Deposition of 15 nm and 50 nm-thick metal layers increases the electrical conductivity of the substrate, improving the deposition kinetics of the CFO precursors and establishing firm contact between CFO and the substrate. CFO films with Ti and Ni underlayers (Ti/CFO and Ni/CFO) exhibit higher photocurrent generation than bare CFO, owing to the rapid charge transfer and low interfacial charge-transfer resistance. Despite comparable apparent solar-to-chemical conversion (STC) efficiencies (∼1%), the C1 chemical (formate) is the sole product in the bare CFO film, whereas mixed C1–C4 chemicals are produced in Ti- and Ni-underlayered CFO films. When estimated based on transmitted light, the Ti/CFO and Ni/CFO films exhibit STCs of ∼7% and 3%, respectively.
Probing Charge Carrier Behavior in Engineered Photocatalysts with Time-Resolved Visible to Mid-IR Absorption Spectroscopy
2023, Journal of Physical Chemistry C
Activated Carbon-Embedded Reduced Graphene Oxide Electrodes for Capacitive Desalination
2023, Journal of Electrochemical Science and Technology

View all citing articles on Scopus

View full text

Solar remediation of wastewater and saline water with concurrent production of value-added chemicals

Highlights

Abstract

Graphical Abstract

Section snippets

Sun-water-energy nexus

Solar conversion systems

Production of reactive oxygen species for wastewater oxidation

Solar treatment of saline water

Summary

Declaration of Competing Interest

Acknowledgements

Catal. Today

Catal. Today

Nano Energy

J. Photochem. Photobiol., C.

Appl. Catal. B

Appl. Catal. B

Nano Energy

Appl. Catal., B

Electrochim. Acta

Appl. Catal. B

Appl. Catal. B

Appl. Catal. B

J. Photochem. Photobiol. A

J. Catal.

Electrochim. Acta

Catal. Today

Appl. Catal. B

Catal. Today

Appl. Surf. Sci.

Solar water splitting cells

Chem. Rev.

Recent advances in solar-driven carbon dioxide conversion: expectations versus reality

ACS Energy Lett.

Monolithic cells for solar fuels

Chem. Soc. Rev.

Artificial photosynthesis: solar splitting of water to hydrogen and oxygen

Acc. Chem. Res.

Technical and economic feasibility of centralized facilities for solar hydrogen production via photocatalysis and photoelectrochemistry

Energy Environ. Sci.

A comparative technoeconmic analysis of renewable hydrogen production using solar energy

Energy Environ. Sci.

Summary of electrolytic hydrogen production: milestone completion report, National Renewable Energy

Lab. (NREL/MP-

General techno-economic analysis of CO2 electrolysis systems

Ind. Eng. Chem. Res.

Advantages of solar hydrogen compared to direct carbon dioxide reduction for solar fuel production

ACS Energy Lett.

The low concentration of CO2 in the atmosphere is an obstacle to a sustainable artificial photosynthesis fuel cycle based on carbon

ACS Energy Lett.

Hydrogen peroxide production from solar water oxidation

ACS Energy Lett.

Photocatalytic water splitting: recent progress and future challenges

J. Phys. Chem. Lett.

Sequestration of atmospheric CO2 in global carbon pools

Energy Environ. Sci.

Domestic wastewater treatment as a net energy producer - Can this be achieved?

Environ. Sci. Technol.

The future of sewater desalination: energy, technology, and the environment

Science

Urea-based fuel cells and electrocatalysts for urea oxidation

Energy Technol.

Urea as a hydrogen carrier: a perspective on its potential for safe, sustainable and long-term energy supply

Energy Environ. Sci.

Urea electroxidation: current development and understanding of Ni-based catalysts

ChemElectroChem

Recend adances in the electro-oxidation of urea for direct urea fuel cell and urea electrolysis

Water-Energy Interactions in Water Reuse

Highly efficient water splitting by a dual-absorber tandem cell

Nat. Photonics

A monolithic device for CO2 photoreduction to generate liquid organic substances in a single-compartment reactor

Energy Environ. Sci.

Wireless solar water splitting using silicon-based semiconductors and earth-abundant catalysts

Science

Environmental applications of semiconductor photocatalysis

Chem. Rev.

Photoinduced charge transfer processes in solar photocatalysis based on modified TiO2

Energy Environ. Sci.

Interfacial charge transfers of surface-modified TiO2 nanoparticles in photocatalytic water treatment

General techno-economic analysis of CO₂ electrolysis systems

The low concentration of CO₂ in the atmosphere is an obstacle to a sustainable artificial photosynthesis fuel cycle based on carbon

Sequestration of atmospheric CO₂ in global carbon pools

A monolithic device for CO₂ photoreduction to generate liquid organic substances in a single-compartment reactor