Salt Rejection Ability Research Articles

Vertically aligned aerogel with concaved surface topography coupled ordered channel enable efficient solar-driven desalination

Solar-driven desalination has been regarded as a promising energy-saving and sustainable strategy to address the serious freshwater shortage issue. However, its performance is restricted by low solar energy utilization efficiency, water transport, and serious salt deposition. Herein, an efficient solar-driven interfacial evaporator with high solar energy utilization efficiency, fast water transport and robust salt tolerance was developed, via constructing vertically aligned sodium alginate (SA) aerogel with concave surface topography coupled ordered water transport channel structure. Concaved reflecting valley surface was assembled with 3D hierarchical photothermal networks of 2D MXene synergistic 1D carbon nanotube to enhance light absorption capacity. Concaved surface topography with multiple reflective nanostructure (angle 45°, depth 1.5 cm) owns strong sunlight concentration performance, which effectively avoid the light loss and thus enhance the light-absorption over a broad spectrum (0.3–2.5 μm). In another way, hydrophilic SA aerogel with vertically aligned structure, which also provides ordered channels for fast water/vapor transport and high salt rejection ability via strong wicking and diffusion effect. Solar-driven interfacial evaporator with such unique concaved surface topography that coupled ordered valley channels exhibits excellent evaporation rate (2.81kg m−2h−1) and remarkable solar energy utilizing efficiency (98.52 %), while with excellent antibacterial ability during continuously desalination process. Solar-driven interfacial evaporator with unique concaved surface topography coupled ordered valley channels holds great potential in sustainable water purification and desalination.

Basil seed hydrogel incorporated activated carbon as a Capable, Bio-Based, and Cost-Effective interfacial solar steam generator

Utilization of solar energy for desalination and purification of seawater opens up a state-of-the-art way to meet the water needs all around the world specially in coastal cities. Herein, the eco-friendly, low cost and bio-based basil seed (BS) hydrogel is combined with activated carbon (AC) to synthesize activated carbon merged with basil seed hydrogel (AC-BS) composite material. Due to the photothermal property of the AC, the AC-BS composite was used to design an interfacial solar steam generator (ISSG) for water purification. The AC absorbs the sunlight and converts it to the required heat needed for water evaporation and the superhydrophilic BS hydrogel supplies water to the surface causing the high salt rejection ability of the system, in addition, it decreases the required energy for evaporation. The AC-BS is characterized using characterization methods such as EDX and FESEM. The two-dimensional (2D) AC-BS system containing a cotton fiber used to transfer water from the bulk to the surface, a layer of styrofoam as a heat insulator and AC-BS on the surface shows evaporation rate of 1.93 kg m−2h−1. The three-dimensional (3D) AC-BS, designed to solve the solar irradiation angle fluctuation problem during a day and seasons, shows an evaporation rate of 2.70 kg m−2h−1 and an efficiency of about 91 % under 1 sun illumination. The ability of the AC-BS system for saline water desalination and waste water-contaminated dyes as a pollutant treatment is highly acceptable. The AC-BS ISSG can be studied and used on large scales to provide fresh water from saline water.

Enhanced properties of a positive-charged nanofiltration membrane containing quaternarized chitosan through second interfacial polymerization for the removal of salts and pharmaceuticals.

Nanofiltration (NF) membrane technology has been widely used in the removal of salts and trace organic pollutants, such as pharmaceuticals and personal care products (PPCPs), due to its superiority. A positive-charged composite NF membrane with an active skin layer was prepared by polyethyleneimine (PEI), trimethyl benzene chloride, and quaternate chitosan (HTCC) through second interfacial polymerization on the polyethersulfone ultrafiltration membrane. The physicochemical properties of the nanocomposite membrane were investigated using surface morphology, hydrophilicity, surface charge, and molecular weight cut-off (MWCO). The influence of the concentration and reaction time of PEI and HTCC was documented. The optimized membrane had a MWCO of about 481 Da and possessed a pure water permeability of 25.37 L·m-2·h-1·MPa-1. The results also exhibited salt rejection ability as MgCl2 > CaCl2 > MgSO4 > Na2SO4 > NaCl > KCl, showing a positive charge on the fabricated membrane. In addition, the membrane had higher rejection to atenolol, carbamazepine, amlodipine, and ibuprofen at 89.46, 86.02, 90.12, and 77.21%, respectively. Moreover, the anti-fouling performance and stability of the NF membrane were also improved.

Tailoring fully crosslinked polyamide layers on optimized polyacrylonitrile supports via coactive delayed phase inversion and alkaline hydrolysis for brine treatment through pervaporation

A novel method of co-hydrolysis of polyacrylonitrile (PAN) support to host polyamide (PA) formation using coactive delayed phase inversion is presented to synthesize high-performance pervaporation membranes. Pure water in the coagulation bath was replaced with a 1.0 M sodium hydroxide solution maintained at 50 °C, allowing concurrent hydrolysis and delayed phase inversion. The characterization results revealed a smoother surface morphology, a higher carboxylic group content, improved hydrophilicity, and an ideal O/N ratio (∼1) of the PA layer on the co-hydrolyzed PAN (HPAN-Co) support compared with the PA layer on the post-hydrolyzed PAN (HPAN-Post) support. Furthermore, the typical pattern observed in PA-HPAN-Post, with a plethora of finger-like pores followed by macrovoids, completely disappeared and was replaced by a uniform and fine microvoid structure in PA-HPAN-Co, with an approximately 50 % reduction in membrane thickness. This led to a reduction in membrane swelling and salt transport without compromising the permeation flux. The pervaporation tests with a 10 wt% NaCl feed at 70 °C using PA-HPAN-Co showed a 99.97 % salt rejection ability and a 74.2 kg m−2h−1 flux, which is 33 % higher than the permeate flux of PA-HPAN-Post. Thus, the PA-HPAN-Co membrane is highly recommended for pervaporative desalination, considering the enhanced performance and scalability of the synthesis technique.

Carbon coated vermiculite aerogels by quick pyrolysis as cost-effective and scalable solar evaporators

Purification of seawater and wastewater by solar-driven interfacial evaporation is a promising way to alleviate water scarcity. However, the high cost, complex fabrication methods, and short service life of the materials limit their practical application. Herein, a novel three-dimensional (3D) photothermal aerogel composited of vermiculite nanosheets and polyvinyl alcohol (PVA) precursors have been prepared via freeze-drying and treated by quick pyrolysis for highly efficient solar-driven interfacial evaporation. The vermiculite nanosheets exfoliated from natural clay were used as the skeletal support of the composite aerogels, which are cheap and abundant natural materials. The introduced PVA improves the mechanical properties and produces carbon derivatives after pyrolysis, enhancing the light absorption capacity. The as-prepared aerogels have hierarchical porous structures, impressive mechanical properties, great light absorption capacity, and outstanding salt-rejection ability. The optimized aerogel not only exhibits a high evaporation rate of 2.64 kg m−2 h−1 (normalized to top and side surfaces) under 1.0 sun irradiation with excellent cost-effectiveness at 361.64 g h−1 $−1 but also shows superior performance in treating high-salt (15.0 wt%) brine water and organic dye-contained wastewater. The proposed method provides an attractive and effective way to prepare photothermal aerogels for efficient solar steam generation for mitigating water scarcity issues.

Scalable, Green, and Cost-Effective Carbonized Sand for Efficient Solar Desalination.

Nowadays, sweet and drinkable water shortage is a global issue which has attracted widespread attention. Desalination of seawater as the greatest source of water on our planet using solar energy as the most abundant and green energy source for producing fresh water can help us address this issue. Interfacial solar desalination is a state-of-the-art, sustainable, green, and energy-efficient method that has been studied lately. One of the key parameters for researching this method with reasonable efficiency is a photothermal material. Herein, carbon-coated sand was synthesized using abundant, green, and low-cost materials (sand and sugar), and its performance as a photothermal material is investigated and reported. In this work, a three-dimensional (3D) system is introduced to develop the performance and efficiency of the system under real sun irradiation and natural circumstances. The salt rejection ability of the system is another important thing we should notice due to the high salinity of seawater that we want to desalinate. The superhydrophilic carbonized sand demonstrated a good evaporation rate of 1.53 kg/m2h and 82% efficiency under 1 sun irradiation and upright salt rejection ability, which exhibited its capability to be used in green solar-driven water vaporization technology for sweet water production. The effects of important parameters, including light intensity, wind speed, and environment temperature, on the evaporation rate using carbonized sand as a solar collector in a solar desalination system were studied in both laboratory and real systems.

Commercial black dye without plasmonic effect: A low-cost viable candidate as a solar absorber for photo-thermal interfacial evaporation and desalination?

Despite the full-spectrum absorption of solar incident, plasmonic metal-based materials and carbon-based materials still suffer from the drawbacks of risk for leakage to bulk water, fragility and high-cost preparation processes in long-term desalination. However, without the characterizations of strong conductivity and plasmonic effect, the black dye with clour of black is unable to achieve broadband absorption over the full-wave spectrum. For this reason, nearlly all of the effort has been continually devoting to seek conductive materials, neglecting the black dye which is colour of black but nonconducting. In this context, commercial low-cost black dye, which is conventionally used to dye fabric with durable black colour, was employed conclusively as an absorber to examine its viability in the field of photo-thermal interfacial evaporation for the first time. By choosing commercial artificial suede as the dying subject, a black-coloured photothermal film (BCPF) fabricated by a fairly low-cost black colorant and very facile staining method features superior wettability, stability (treated by ultrasonic agitation for at least 15 h without any fading) and performance in photo-thermal conversion. Evaporation tests show that the evaporation rate of BCPF-based evaporators can reach as high as 1.85 kg m−2 h−1. Furthermore, a strategy of laying under BCPF a layer of CAS film can greatly improve the salt-rejection ability of the evaporation device, not only causing dramatic degradation of the evaporation performance hardly but also contributing to environmental sustainability. In summarry, this study demonstrates the black dye as solar absorber for promising sustainable desalination, and also paving a way for the future exploration of practical new type photothrmal materials for interfacial evaporation.

Potato-based microporous carbon cake: Solar radiation induced water treatment

The use of solar-driven interfacial water evaporation for water desalination is a very interesting research topic for its high-performance water purification. The rapid evaporation of water at the air-water interface has been enhanced by solar absorbers. This work described the fabrication of a porous carbon cake with interconnected pores and super-hydrophilic surfaces from a potato slice. The fabricated carbon cake exhibits a high steam generation rate of 3.18 kg m-2 h-1 under 1 sun illumination. We also fabricated a large area evaporator and demonstrated the collection of more than 2.8 lit of condensed water from 0.8 m2 area in 5.5 h with natural (∼0.5 Sun) solar illumination. High evaporation rate was obtained due to the super-hydrophilic and less thermal conductivity of the as-fabricated carbon cake. Moreover, the device providing a high mechanical stability, which could be necessary for long-term potential usage. The high salt rejection ability of the device were investigated in detail. The total cost to generate freshwater from CEPC STE for nearly 8 months is $ 36.54/m2. Therefore, this system can be used for evaporation-based high concentrated dye and brine water purification in a cost-effective and highly efficient way.

Fabrication of graphene-oxide and zeolite loaded polyvinylidene fluoride reverse osmosis membrane for saltwater remediation

Incorporation of inorganic and organic materials in polymer has contributed well towards the development of advanced reverse-osmosis membranes; with greater permeation, and salt rejection potential. We are reporting, Zeolite/GO/PVDF based thin-film composite membranes that were successfully synthesized by solution casting process, an eco-friendly, low-cost, and biocompatible technique. PVDF membranes modified with different ratios of GO/Zeo (0.03, 0.05 and 0.07) were characterized by FTIR, SEM, XRD, TGA, and DSC. Membranes were then tested for its potential for water permeation and salt rejection abilities. As prepared membranes owe better pore-distribution, a moderate degree of crystallinity and high absorption capability that is highly needed for micro-filtration phenomena used for desalination of saline water. The modified membranes exhibited enhanced water permeability up to 28.9 L/m2h as compared to pure PVDF membrane having water permeability flux of 15.6 L/m2h. Salt-rejection ability was found increasing for the membranes (up to 98%) modified with different concentration of GO/Zeo, as compare to pure PVDF membrane (82%). During water permeation and salt rejection studies, no deleterious impact was noted for modified PVDF membranes. This development will entail an efficient approach to furnish high-level performance reverse-osmosis membranes, with greater osmotic-pressure bearing capacity and higher stability.

A high stability GO nanofiltration membrane preparation by co-deposition and crosslinking polydopamine for rejecting dyes.

In order to improve the stability of nanofiltration membrane in separation and purification, a novel polyelectrolyte multilayer nanofiltration membrane was facilely prepared by co-deposition of polydopamine (PDA) and polyethyleneimine (PEI) on the polyethersulfone (PES) ultrafiltration membrane substrate, followed by immersing graphene oxide (GO) solution, and crosslinking PDA. The modified surfaces were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM), water contact angle, their saline flux and ability to reject salt and dye were determined. The results also exhibited salt rejection ability as Na2SO4 > K2SO4 > MgSO4 > NaCl > KCl > MgCl2, suggesting the higher rejection of divalent anion. Also, the retention order of the dye by the GO modified membrane is DY86 > DB19 > AG27 > DY142 > DB56 > AR151 > VB5, indicating that the GO modified membrane has better rejection of negatively charged dyes as well as higher molecular weight dyes. Ethanol and hypochlorite resistance tests under different pH conditions showed the membranes coated GO enhanced stability in regard to salt rejection properties. Significantly, the anti-biological test confirmed the growth rate of microalgae on the GO introduced membrane was decreased greatly due to enhanced stability and lower roughness.

A self-regenerating 3D sponge evaporator with a tunable porous structure for efficient solar desalination

Bottom-up design of 3D evaporator with high water evaporation rate shows excellent salt-rejection ability for effective and perpetual solar desalination system.

Environmentally Friendly and Efficient Hornet Nest Envelope-Based Photothermal Absorbers.

Water shortage is a critical global issue that threatens human health, environmental sustainability, and the preservation of Earth’s climate. Desalination from seawater and sewage is a promising avenue for alleviating this stress. In this work, we use the hornet nest envelope material to fabricate a biomass-based photothermal absorber as part of a desalination isolation system. This system realizes an evaporation rate of 3.98 kg m–2 h–1 under one-sun illumination, with prolonged evaporation rates all above 4 kg m–2 h–1. This system demonstrates a strong performance of 3.86 kg m–2 h–1 in 3.5 wt % saltwater, illustrating its effectiveness in evaporation seawater. Thus, with its excellent evaporation rate, great salt rejection ability, and easy fabrication approach, the hornet nest envelope constitutes a promising natural material for solar water treatment applications.

Environmentally safe and renewable solar vapor generation device based on Prussian blue nanoparticles immobilized on cellulose nanofibers

Solar vapor generation is a sustainable solution to overcome the shortage of fresh water. Although several solar vapor generation devices showing significant evaporation rates have been developed over the past years, there are still remaining problems such as fabrication difficulties and potential environmental hazards. In this report, we demonstrate a solar evaporation device composed of agar hydrogel (AHG) and Prussian blue (PB) immobilized on cellulose nanofiber (CNF). The CNF-PB/AHG device shows a high evaporation rate of 2.22 kg m−2 h−1 under one sun illumination arising from the combined effects of the high water-transport performance of CNF/AHG and the good photothermal ability of PB. The device does not exhibit salt fouling or any decline in desalination performance under a long-term day and night simulation due to the salt-rejection ability of AHG. The average fresh water generation in the field test is 5.95 kg m−2 day−1. Furthermore, the used device can be resurrected without decline of the vapor generation performance through a simple re-fabrication process due to the remarkable stability of CNF-PB and reversible sol-gel transition of AHG. In conclusion, the CNF-PB/AHG device is an environmentally safe, low-cost, easily manufacturable, and renewable solar desalination system.

Tailoring the properties of polyamide thin film membrane with layered double hydroxide nanoclay for enhancement in water separation

This current paper presented a new candidate and potentially to improve the current membrane materials in water filtration process. With that, the primary materials used in this research study is layered double hydroxides (LDH) nanoclay which can be obtained from earth minerals and self-synthesized from inorganic salts were discussed thoroughly to help a better understanding of these materials. However, the current technologies of water separation were still lagging behind and ineffective especially in removal of divalent metal ions and multivalent salts. Infeasibility of reverse osmosis membrane make it not a viable option for divalent salts filtration. With that, nanofiltration (NF) membrane offered as an alternative to substitute available method. In this study, thin film nanocomposite (TFN) membranes were fabricated by incorporating layered double hydroxides (LDH) nanoclay. The LDH nanoclay with different loading ratio of 0, 0.05, 0.1, 0.15 and 0.2 were impregnated into polyamide layer on top of polysulfone substrates. The fabricated TFN were characterized in terms of physicochemical properties (SEM and FTIR) and membrane hydrophilicity (contact angle). After the addition of LDH, the morphological structures of TFN membranes were changed and the surface hydrophilicity was enhanced significantly. FESEM images displayed a typical ridge and valley morphology with nodule-like structures. As the LDH loading was increased, the contact angle decreased from 34.56° to 15.76° showing the surface hydrophilicity of membrane is improved. The separation performance of membrane was evaluated in terms of salt rejection ability by cross flow filtration system. The best performance NF membrane was found to be TFN 0.05 with high water flux and MgCl2 rejection with values of 24.18 L/m2.h and 91% respectively. This study has experimentally validated the potential of LDH materials in membrane process for improvement in water separation process.

Promoting the separation and antifouling properties of polyethersulfone-based nanofiltration membrane by incorporating of cobalt ferrite/activated carbon composite nanoparticles

In this study, a mixed matrix polyethersulfone-based nanofiltration membrane was prepared by incorporation of (cobalt ferrite/activated carbon) composite nanoparticles. The composite nanoparticles were also synthesized using the chemical precipitation technique. The FTIR, XRD and FESEM were used to characterize the synthesized nanoparticles. The fabricated membranes were also studied using SEM, 3D surface image, and water contact angle, mean pore size and porosity measurements. The water flux, salt rejection and antifouling ability of membranes were investigated. The blended membranes showed a more hydrophilic and smoother surface compared to the pristine membrane. The membrane PWF was declined initially using 0.05wt. % (CoFe2O4/AC) nanoparticles into membrane body and then enhanced by a further increase of nanoparticles’ concentration up to 0.1wt. % in membrane matrix; PWF was reduced again for the blended membranes at higher concentration of nanoparticles. The NaCl and Na2SO4 rejections were enhanced from (42% to 85%) and (55% to 95%) by the use of (CoFe2O4/AC) nanoparticles into the membrane body. The blended membranes also exhibited appropriate anti-fouling property and more stable flux compared to the pristine membrane. The highest Pb2+, Ni2+, and Cu2+ rejections were found 86%, 90%, and 97%, respectively, for the blended membrane containing of 1wt. % (CoFe2O4/AC) compared to others.

Hybrid Photovoltaic-Thermal Solar System for Brackish Water Reverse Osmosis

In this paper, a hybrid combination of solar thermal collector and photovoltaic (PV) solar system was applied to reverse osmosis (RO) desalination plant to increase the energy efficiency and its sustainability. An experimental study was performed on 75 GPD small scale RO plant using processed brackish/saline groundwater in Kenjeran area. It shows that increasing in temperature of feed raw water results a decrease in pump pressure and the consumption of electrical power. The smallest result of pump pressure which is 40 psi and the smallest electrical power consumption which is 1.68 W were obtained when the temperature is at 40 °C. However, the quality of the product, the amount of water, and the ability of the membrane to recover salt are decreasing when the temperature of the feed water is raised. The best result was obtained at 31 °C with a TDS water product quality of 105 ppm, the amount of produced water was 36.5 L, and a salt rejection ability was 95.9%. The electrical power consumption of whole system for one day was 914.63 Watt-hours and requires six units of 155 Watt-peak capacity of PV panels.

Salt-resistant carbon dots modified solar steam system enhanced by chemical advection

Salt deposition still remains a significant challenge due to the decreasing evaporation efficiency of solar desalination. Herein, we provide a salt-rejection model coupled with the experimental verification about the chemical diffusion or advection process for solar steam generation. The designed evaporating system established by in-situ polymerization (polypyrrole) of carbon dots modified MnO2 nanowires coated on non-woven cotton fabric decorated ultra-flexible and super hydrophilic polyurethane foam (30% wicking). The salt-rejection investigations reveal real-time chemical advection phenomena where hot brine flows from the top surface to underneath water through a salinity gradient with the aid of accumulated heat. The prototype demonstrates an excellent salt rejection ability within a minimum record time (2 g/100 min) or once soaked (2 g/60 s). The floatable solar-driven evaporator exhibits incredible flexibility (80%, compressive strain) along with an evaporation rate of 1.68 kg m−2 h−1, and photothermal conversion efficiency (∼96.4%, solar to vapor) from high-salinity brine (10 wt %) and wastewater containing heavy metal ions (30 wt%). The outdoor test revealed a yield of 13.60 kg m−2 in one sunny day that provides a potential solution to single-step drinking water supply from various resources of the sea, lakes, and mixtures of emulsified oil, bacterial pathogens, and industrial wastewater.

Positively charged poly (N-vinyl imidazole) gel-filled loose nanofiltration membranes: Performances and modelling analysis

Loose nanofiltration (NF) membrane with pore radius approaching 1 nm and positive charges can be valuable alternative to commercial available negatively charged polyamide NF membrane in specific applications, such as removal of hardness and heavy metal ions and selective separation of dyes/salts mixture. In this work, positively charged poly(N-vinyl imidazole) (PVI) gel-filled loose NF membranes were developed by asymmetric gel-filling upon an asymmetric ultrafiltration (UF) support via UV-initiated surface grafting polymerization and post-quaternization. Compared to the polyamide NF membranes, these membranes displayed a comparable salt rejection ability due to their stronger Donnan exclusion effect. A rigorous three-parameter transport model (TPM) considering steric, Donnan and dielectric exclusion on ions partitioning via effective pore radius (rp), membrane charge density (Xd) and averaged pore dielectric constant (εp), was used to analyze the membrane parameters. Then the gel conformation model (GM) treating confined gel as semi-dilute polymer solution with a characteristic correlation length (ξ) was applied to analyze these gel composites. The results suggest that the gel polymer volume fraction (φ) is decisive in the gel mesh size (viewed as membrane pore size) and gel permeability. Surface porosity of the asymmetric UF base is a limiting factor in membrane permeability. The joint modelling analysis can clarify the membrane structure-properties relationship, performance limits and potentials of the gel-filled NF membrane and hence facilitate structure design and optimization.

A MXene‐Based Hierarchical Design Enabling Highly Efficient and Stable Solar‐Water Desalination with Good Salt Resistance

AbstractA solar‐thermal water evaporation structure that can continuously generate clean water with high efficiency and good salt rejection ability under sunlight is highly desirable for water desalination, but its realization remains challenging. Here, a hierarchical solar‐absorbing architecture is designed and fabricated, which comprises a 3D MXene microporous skeleton with vertically aligned MXene nanosheets, decorated with vertical arrays of metal–organic framework‐derived 2D carbon nanoplates embedded with cobalt nanoparticles. The rational integration of three categories of photothermal materials enables broadband light absorption, efficient light to heat conversion, low heat loss, rapid water transportation behavior, and much‐improved corrosion and oxidation resistance. Moreover, when assembling with a hydrophobic insulating layer with hydrophilic channel, the MXene‐based solar absorber can exhibit effective inhibition of salt crystallization due to the ability to advect and diffuse concentrated salt back into the water. As a result, when irradiating under one sun, the solar‐vapor conversion efficiency of the MXene‐based hierarchical design can achieve up to ≈93.4%, and can remain over 91% over 100 h to generate clean vapor for stable and continuous water desalination. This strategy opens an avenue for the development of MXene‐based solar absorbers for sustainable solar‐driven desalination.

Polyamide‐based membranes consisting of nanocomposite interlayers for high performance nanofiltration

AbstractIt is still a task to synthesize polyamide‐based membranes with selective layers down to 10–20 nm for high performance desalination. Herein, cellulose nanocrystals (CNC) were used as one‐dimensional (1D) nanorods and graphene oxides (GO) as two‐dimensional (2D) nanosheets, respectively, to construct nanocomposite interlayers for synthesizing polyamide layers thinner than 15 nm. The 2D nanosheets are homogeneously mixed with the 1D nanorods and effectively reduce the surface roughness of the nanocomposite interlayers with decreasing the mass ratio of CNC/GO. Polyamide layers with a thickness of 10–15 nm have been synthesized at an ultralow monomer concentration of 0.025 wt% on these CNC/GO nanocomposite interlayers. The polyamide‐based membranes exhibit extremely high water permeation (45.9 L/m2·h·bar) without losing their salt rejection ability. The nanofiltration performances of these polyamide‐based membranes are higher than most of the reported nanofiltration membranes in recent years.